Gribben Davies Machine tools ltd

Condition: good (used), Year of construction: 2004, NAGEL/TBT BW-30-3000 Deep Hole Drilling Machine Year of manufacture: 2004 Control: SIEMENS SINUMERIK 840D Drilling depth up to 3,000 mm Maximum drilling diameter: max. 27 mm / min. 16 mm Axes: 3 Maximum feed: 140 mm/min Table axis X: 950 mm Working area in X axis: 900 mm Working area in Z axis: 1,750 mm Coolant capacity: 2,400 l Table load capacity: 4,000 kg Cooling system type: KA-1 Table size: 3,300 x 950 mm Feed rate up to 7,000 mm/min Power output N = 7.5 kW Speed: 650 - 6,500 rpm Automatic central lubrication Hydraulic drive for boring bar guide sleeve Magnetic chip conveyor All other accessories visible in the photos and video are not included in the scope of delivery and therefore not part of this sale. The scope of delivery only includes the accessories explicitly listed here, in the order confirmation and invoice. Cedex Aglcopfx Aflsaa FCA (Free Carrier Loaded Truck) D-95447 Bayreuth Packaging only Delivery time: immediately Subject to prior sale / Payment due immediately upon purchase

Condition: repair required (used), Year of construction: 1991, functionality: limited functionality, machine/vehicle number: 950082, drilling depth: 1,000 mm, travel distance X-axis: 1,500 mm, type of input current: three-phase, This machine is equipped with a Bosch CC100 M control system and has a defect. All motors and the drive are in working condition. The machine can be used for retrofit or as a source of spare parts. Codpfxox Afbpe Afloaa

Condition: excellent (used), Year of construction: 2003, Deep Hole Drilling and Milling Machine TBFZ 1600 CNC Year of manufacture: 2003 X-AXIS TRAVEL: 1600 MM Y-AXIS TRAVEL: 1200 MM Z-AXIS TRAVEL: 500 MM W-AXIS TRAVEL: 1200 MM B-AXIS TRAVEL: 360° (Rotary table) Cedoxz Aygspfx Aflsaa * Table size (LxW): 1500x1500 mm * T-slots: 5x DIN 650-22 h12, 150 mm spacing * Tool clamping: hydraulic * Electrical connection: 400 V, 50 Hz * Compressed air connection: rated flow rate 7000 l/min, operating pressure: 6 bar * Botek driller optionally available * Feed drive: brushless AC servo motors * Feed rate: 0-20000 mm/min * Rapid traverse: X 20000 mm/min, Y+Z 20000 mm/min * Manual mode: 20000 mm/min * Setup operation: 0-2000 mm/min

Condition: good (used), Year of construction: 2017, functionality: fully functional, Technical details core drilling diameter max. 3 - 28 mm bore depth 1000 mm control Heidenhain TNC 640 x-axis 1000 mm y-axis 800 mm z-axis 800 mm spindle head - swivable (W) +15°/-30° deg B-axis (table) 360.000° deg table surface area 1000 x 1000 mm table load 5,0 t tool taper SK 40 spindle turning speed range 60 - 6000 U/min spindle motor 12 kW total power requirement 58 kW weight of the machine ca. 14 t dimensions of the machine ca. 6,35 x 4,75 x 3,80 m Additional information 5 axes Deep Drilling-Milling-Machine A current geometry measurement report is available. Equipped with: HEIDENHAIN TNC 640 control 5 CNC AXES X – Y – Z – W – B NC rotary table 360.000 deg. Milling performance 150 cm3/min. Direct linear position measuring system Digital AC drives Table design with Hirschmann zero-point clamping system NC-controlled tilting of the deep hole drilling/milling unit (W) +15/-30 deg. Automatic tool changer for 24 tools Internal coolant supply High-pressure coolant system 1200 liters for deep hole drilling oil up to 140 bar Paper belt filter system SIEMENS extinguishing system Fire protection system Spindle cooling Oil temperature control 3D HEXAGON probe RENISHAW tool measurement Electronic handwheel OPT kinematics Chip conveyor Coolant pressure and flow control Collision and vibration monitoring Feed control Csdpfx Asxztd Njfljaa Coolant gun MONTRONIX machine airbag Oil mist extraction 2 clamping plates Walk-in full enclosure with roof and opening for crane loading Included in delivery: Operating manual Documentation Machine parameters on USB stick

Condition: like new (used), Year of construction: 2019, operating hours: 454 h, functionality: fully functional, machine/vehicle number: 7438, drilling depth: 3,000 mm, total length: 11,515 mm, total width: 5,415 mm, total height: 2,350 mm, overall weight: 14,450 kg, spindle speed (min.): 13 rpm, spindle speed (max.): 1,800 rpm, rapid traverse Z-axis: 6,000 m/min, type of input current: AC, input voltage: 400 V, Deep drilling machine, in excellent conditions due to very limited usage - 454 hours. Tooling of different diameters available and included in the price. Selling because of business change. Cjdpsxzq Ryjfx Aflsaa

Condition: like new (used), Ryazan Model PT295106 Deep Hole Borer x 4000mm Manufacturer Ryazan Casdpfx Asxzp Rloflja Model PT295106 Year 1985 Condition Used Stock Number 2850 Centre Height 550mm Solid Boring Capacity 200mm Max Boring Length 4000mm Headstock Hollow spindle 500mm Headstock Spindle speeds 16-250 rpm Headstock drive 50/75kw Max boring length in front of headstock 3500mm Max boring length if using the 500mm hollow spindle 4000mm

Condition: excellent (used), Year of construction: 2012, operating hours: 79,000 h, functionality: fully functional, machine/vehicle number: 106648-11, Please provide your offer price. Sales only within Europe, including Turkey. Price excluding packaging; delivery condition: FCA (machine location). Caedpfx Afsxzgraslea Available machines: 5 units, identical process. Year of manufacture: 2001 - 2012 ===== For technical data, please refer to the handout. All warranty rights are excluded. We do not guarantee the accuracy of the technical data and year of manufacture, the completeness of accessories and tooling, or compliance with all safety and environmental protection requirements specified in accident prevention regulations. No sale to private individuals.

Condition: good (used), functionality: fully functional, Deep Hole Drilling Machine MEWAG - IXION TL 500 - Drilling depth approx. 500 mm - Table size 800 x 450 mm - Support / drilling table rotatable, angle-adjustable 0-360 degrees - Drilling stroke - manual - Various deep hole drill bits included Cjdpfx Aexzd Tnjflsaa - Connection cable live, ready for demonstration Dimensions: LxWxH 1.6 x 0.8 x 1.6 meters / Weight 1300 kg Subject to errors and input mistakes

Condition: excellent (used), Year of construction: 2018, travel distance X-axis: 2,000 mm, travel distance Y-axis: 1,600 mm, travel distance Z-axis: 1,800 mm, Table 1,500 x 1,500 mm X 2,000 mm Y 1,600 mm Z 1,800 mm B-axis, A-axis swiveling +/- 19 degrees Machine features full enclosure Chip conveyor and high-pressure coolant system Tool holder SK 50 Control Heidenhain iTNC 640 Table load capacity 20 tons Spindle speeds up to 4,000 rpm Caedpfexyic Sjx Aflja Rapid traverse 20 m/min Tool changer with 40 stations

Condition: excellent (used), Year of construction: 2007, • Maximum possible drilling depth: 1200 mm • Maximum hole diameter: 32 mm • Minimum drilling diameter: 6 mm • Longitudinal travel (X-axis) table: 1800 mm • Cross travel (Z-axis) column: 1700 mm • Cross travel (W-axis) drilling head: 1150 mm • Vertical travel (Y-axis) drilling head: 1200 mm • Clamping surface NC table: 1500 x 1000 mm • Maximum table load: 10 t • Rotary axis (B-axis) rotary table: 360° • Rotary axis (A-axis) drilling head: -25°/+15° • Feed rate: 1-15 m/min (Y-axis: 1-10 m/min) • Rapid traverse speed in all axes: 15 m/min (Y-axis: 10 m/min) • Maximum spindle speed: 6000 rpm • Minimum spindle speed: 60 rpm • Tool holder: SK 40 • Tool clamping: OTT • Rated power main drive (100% ED, S1/40% ED, S6): 9/13 kW • Coolant tank capacity: 1000 l • Maximum coolant pressure: 100 bar • Low-pressure external and high-pressure internal coolant supply • Power supply: 3x 400 V; 50 Hz • Required installation space (L x W x H): 6550 x 5350 x 4130 mm • Machine weight: 12,000 kg Deep Hole Drilling Machine Equipment • CNC control: HEIDENHAIN iTNC 530 • Interpolated rotary table with minimal backlash, dimensions 1500 x 1000 mm • Swiveling drilling head +15°/-25° • Shank drilling head • Handwheel HR520 • Fixed supports (2 units) • Tool magazine: ELB tools: 12 pcs (max. diameter: 32 mm / max. length: 1550 mm) Standard tools: 12 pcs (max. diameter: 140 mm / max. length: 400 mm) • Direct measurement and positioning system in X, Y, and Z axes • Collision monitoring system for supports and drill sleeves • Oil cooler • Coolant flow control system • Adjustable coolant nozzles • Cooling unit for electrical cabinet • Enclosed upper cover (roof) • Drip tray for machine and tank facility (tray height 30 mm) Caodpfx Ajxyf E Nofloa • Extraction system • Infrared touch probe • Drilling depth extension 1200 mm (retrofit) • Chip conveyor

Condition: excellent (used), Year of construction: 2016, operating hours: 40,000 h, functionality: fully functional, Technical data: 3 x drilling spindles Boring method: BTA Minimum drilling diameter: 18 mm Maximum drilling diameter: 30 mm Maximum drilling depth: 1800 mm Rotating tailstock, hydraulic with counter-rotation, stroke 45-50 mm Spindle distance: 210 mm Feed rate: 1-4000 mm/min Position display with 1-axis PLC deep hole drilling control and monitoring Cjdpfx Afoxyarwjlsaa Gear motor with holding brake for counter-rotation of workpieces, 160 rpm Chip conveyor Oil trough with extraction pump

Condition: used, Year of construction: 1983, operating hours: 6,348 h, functionality: fully functional, drilling depth: 1,500 mm, total length: 5,000 mm, total width: 2,600 mm, total height: 2,000 mm, overall weight: 6,000 kg, travel distance X-axis: 1,250 mm, travel distance Y-axis: 900 mm, travel distance Z-axis: 900 mm, spindle speed (min.): 100 rpm, spindle speed (max.): 6,000 rpm, table length: 1,000 mm, table width: 1,000 mm, Max. table load: 3,000 kg Drill diameter: 5–50 mm Taper: SK 40 Control: Siemens 802 D Machine overhauled: 2009 Codpsxx Tr Uofx Afljaa

Condition: excellent (used), bore depth 500 mm spindle speed: 1 Cajdpfxexx A D Tj Aflea

Condition: excellent (used), Year of construction: 2001, drilling depth: 700 mm, travel distance X-axis: 1,600 mm, travel distance Y-axis: 1,200 mm, travel distance Z-axis: 1,600 mm, spindle speed (min.): 6,000 rpm, drill diameter: 40 mm, table length: 1,500 mm, table width: 1,250 mm, table load: 10,000 kg, Year of manufacture: 2001 Control: Heidenhain TNC 430 X: 1600 mm Caedpfxjxu Dkge Aflsa Y: 1200 mm Z: 1600 mm W: 500 mm Table: 1500*1250 mm, 10T B-axis, A-axis swiveling +/- 19 degrees Machine features full enclosure Chip conveyor with coolant system Tool holder: SK50 Tool changer: 20 positions

Condition: used, Year of construction: 2007, Control unit, manufacturer Selca, type S40-45DH, 7 axes (X/Y/Z/W/V/B), rotary table 1,000 x 800 mm, travel X/Y/Z 1,650 x 1,000 x 380 mm, W 500 mm, V 1,000 mm, B 360x0.001°, drilling diameter 6-22 mm, drilling spindle 9 kW, max. speed 4,200 rpm, milling spindle 9 kW, max. speed 2,000 rpm, 20-position tool changer, tool holder ISO40, oil mist extraction unit, manufacturer Sey, cooling unit, manufacturer Eurocold, type Ecological Line, chip conveyor, tool and accessory package, workbench, small workbench, tool trolley, 6 drawers, WTS rack, 4 levels, contents: setup tools, 70 tool holders SK 40, lot of deep hole drills Cedpfx Afjxugydjlsaa +++ Attention: This machine is part of an online auction! +++

Condition: excellent (used), functionality: fully functional, drilling depth: 1,000 mm, feed length X-axis: 1,650 mm, feed length Y-axis: 1,000 mm, travel distance Z-axis: 360 mm, spindle speed (max.): 4,200 rpm, drill diameter: 40 mm, rapid traverse X-axis: 10 m/min, rapid traverse Y-axis: 10 m/min, rapid traverse Z-axis: 10 m/min, spindle motor power: 10,000 W, table length: 700 mm, table width: 1,400 mm, table load: 4,000 kg, feed length W-axis: 500 mm, Selca S4040D CNC Control Drilling depth, transverse movement V axis: 1,000 mm Column, longitudinal movement X axis: 1,650 mm Drilling slide, vertical movement Y axis: 1,000 mm Drilling slide, workpiece support movement W axis: 500 mm Drilling slide, maximum vertical "swivel" - A axis: +20° / –20° Rapid traverse, adjustable speed up to 10,000 mm/min Drilling diameter in solid material min/max: 5 – 40 mm Drilling spindle, rotational speed, adjustable: 1 – 4,200 rpm Drilling spindle motor power: 10 kW Cjdpfx Aoxpwf Tsflsaa Fixed clamping table, dimensions: 700 x 1,400 mm Standard clamping slots: 18 mm Hydraulic pump motor power: 7.5 kW Gun drill holder; shank for drills > 6 mm: 10 x 40 mm Gun drill holder; shank for drills < 6 mm: 25 x 70 mm Clamping table ROTARY & "BARRASENO" axis B Dimensions mm: 800 x 1,000 Standard clamping slots: 18 mm Maximum axial load (rotary): 4,000 kg Continuous rotary axis B resolution: 360,000 steps/rev Maximum vertical resolution "BARRASENO" axis B1: +20° / –20° Small milling head – threading, etc. Maximum horizontal working stroke Z axis (830): 360 mm Spindle speed, adjustable up to 2,200 rpm Threading spindle motor power: 10 kW ISO40 tool changer with 10 rotary-translating stations USED MACHINE

Condition: refurbished (used), Year of construction: 2000, functionality: fully functional, drilling depth: 600 mm, rotational speed (max.): 6,000 rpm, center height: 250 mm, controller model: SIEMENS Sinumerik 840 D, workpiece diameter (max.): 25 mm, No reserve price – guaranteed sale to the highest bidder! The machine has been completely overhauled! TECHNICAL DETAILS Working depth: 600 mm Working diameter: 4 – 25 mm Number of spindles: 2 Centre height: 250 mm Centre distance: 203.2 mm Speed range: 1,000 – 6,000 rpm Feed rate: 0 – 300 mm/min Rapid traverse: 6,000 mm/min MACHINE DETAILS Control system: SIEMENS Sinumerik 840 D (Retrofit) Drilling system: Single-lip deep hole drilling Main drive: 2 x 5.5 kW EQUIPMENT - Single functions for machine setup - Semi-automatic operation for manual loading - Robust spindle carriage - Machine monitoring with spindle speed display - Table plate in special cast design - Safety guard with sliding door - Machine bed with hardened and ground linear guides Caodpfxsxpvbto Aflja - Internal coolant supply through drilling spindle - Electrical equipment according to IEC standards - Separate control cabinet with safety devices - Control panel in working area

Condition: ready for operation (used), Year of construction: 1979, functionality: fully functional, machine/vehicle number: 419.324.012, drilling depth: 1,200 mm, spindle speed (max.): 3,000 rpm, table length: 1,050 mm, table width: 1,050 mm, center height: 1,040 mm, No minimum price – guaranteed sale to the highest bidder! The payment deadline for the machine is 20/11/2025! Placing a bid obligates you to collect the machine on time between 01/12/2025 and 05/12/2025! TECHNICAL DETAILS Drilling depth: 1,200 mm Spindle speed (min): 50 rpm Spindle speed (max): 3,000 rpm Feed rate (Row 1): 18 – 160 mm/min Feed rate (Row 2): 35 – 320 mm/min Rapid traverse speed: 3.5 m/min Rated motor speed: 1,400 rpm Codpfx Afoxm S Idslsaa Table length: 1,050 mm Table width: 1,050 mm Centre height above table: 240 – 1,040 mm MACHINE DETAILS Dimensions (L x W x H): 6,500 x 3,500 x 2,900 mm Electrical data Operating voltage: 380 V Frequency: 50 Hz Connected load: 25 kW EQUIPMENT 3-axis Heidenhain digital readout Coolant system

Condition: ready for operation (used), Year of construction: 2011, functionality: fully functional, machine/vehicle number: 35114, feed length X-axis: 600 mm, feed length Y-axis: 300 mm, feed length Z-axis: 600 mm, spindle speed (max.): 4,000 rpm, drill diameter: 16 mm, No reserve price – guaranteed sale to the highest bidder! The payment deadline for the machine is 20/11/2025! Placing a bid obligates you to collect the machine on time between 01/12/2025 and 05/12/2025! TECHNICAL DETAILS Feed travel X-axis: 600 mm Cedpfxoxm S Hys Aflsaa Feed travel Y-axis: 300 mm Feed travel Z-axis: 600 mm Feed travel W-axis: 650 mm Spindle speed (max.): 4,000 rpm Drilling diameter, twist drill: max. 16 mm Single-lip drill: 4 to 16 mm Tapping: max. M12 Table length: 1,000 mm Table width: 680 mm MACHINE DETAILS Control model: HEIDENHAIN TNC 124 DIMENSIONS & WEIGHT Dimensions (L x W x H): 3,500 x 1,500 x 2,100 mm Total weight: 2,000 kg

Condition: good (used), Bench drill, pillar drill, column drill, column drill -Manufacturer: WMW Heckert, bench drilling machine type BT 2 -Clamping table: 340 x 280 mm -Travel: 350 mm -Spindle holder: MK2 -Projection: 215 mm -Speeds: 355/710/1400/2800 rpm -Column: diameter 93 mm -Spindle stroke: 100 mm / depth stop with fine adjustment -Motor: VEM 0.8/1.0 kW with brake -Voltage: 380 V -Number: 2x drill available -Price: per piece -Dimensions: 550/480/H1270 mm -Weight:157 kg/piece Cajdpfjxm Rzisx Aflsa

Condition: used, Year of construction: 2006, Solid drill diameter / mm bore depth / mm number of spindles / Froriep CNC deep hole drilling machine – the prefabrication specialist Year of manufacture: 2006 Control system: Siemens Sinumerik 840D Cajdpfoxgu R Iox Afloa Max. drilling depth: 8,850 mm Workpiece diameter: 150 – 900 mm Speed range: 1 – 300 rpm Feed rate: 0.5 – 4,500 mm/min Drive power: 129 kW Swing diameter over bed: 1,000 mm Clamping diameter faceplate: 900 mm Weight: approx. 47,000 kg Ideal for precise pre-drilling of deep holes – including faceplate, steering ring

Condition: good (used), Year of construction: 2009, operating hours: 20,709 h, functionality: fully functional, machine/vehicle number: 106516-11, drilling depth: 1,200 mm, overall weight: 7,500 kg, For sale: A very well-equipped deep hole drilling machine from TBT, including various accessories. Drilling specifications: - Spindle 1: 5–18 mm; Spindle 2: 1–4 mm - Drilling depth: approx. 1200 mm with Ø8 mm using 3 steadies - Number of spindles: 2 - Spindle drive: Spindle 1: 1 x 4 kW; Spindle 2: 1 x 1.2 kW Cjdpfjxgnhajx Afleaa - Spindle speed: Spindle 1: 600–6000 rpm; Spindle 2: 2000–24000 rpm - Rapid traverse: 15,000 mm/min - Saddle stroke (nominal): 1800 mm - Coolant: Deep hole drilling oil - Tank capacity: 1,100 liters - Operating voltage: 3AC 400V, 50Hz (Total connected load: 25 kW) Condition: Good, appropriate for its age Accessories: Includes drip tray and various drills On-site inspection is recommended!

Condition: used, Year of construction: 2004, Solid drill diameter 200 mm bore depth / mm number of spindles / Technical data Power: 129 kW Control: Siemens NC control Speed range (stepless): 2 - 300 rpm Feed range (in steps): 3 - 4500 mm/min Oil system capacity: 20,000 litres Maximum delivery rate: 1500 l/min Circular diameter in steady rest: 1100 mm Circular diameter over bed: 1250 mm Centre distance: 11000 mm Clamping diameter face plate: up to 1100 mm Max. workpiece weight with one tailstock: 10 t Clamping range of the two steady rests: 150 - 1100 mm Clamping range BOZA: 1 = 200 - 400 mm 2 = 400 - 800 mm Dimensions Min. outer diameter: 406 mm Max. outer diameter: 850 mm Wall thickness: 10–150 mm Max. workpiece length: 11,000 mm Max. workpiece weight: 10 t Max. strength: 800 N/mm² Specific cutting resistance (Ks): 2000–2100 N/mm² Machine data Machine length: 28,800 mm Centre height: 560 mm Swing diameter over bed: 1120 mm Caedpexgic Ejfx Afloa Full drilling diameter: 200 mm Core drilling diameter: 350 mm Reaming diameter without drilling: 350 mm Reaming diameter with drilling: 350 mm Headstock: Main drive motor: Siemens Type: 1 PH 7228 Performance data at 1,000 min: 113 kW / 1,079 Nm Performance data at 1,150 min: 129 kW / 1,017 Nm Main gearbox: Z-F manual gearbox Type: 2 K210 Switchable gear ratios: i = 1:1 i = 1:4 Fixed gear ratio for spindle: i = 11.68 Max. torque: 50,000 Nm Speed range I: 2...300 min Speed range II: 2 ...75 min

Condition: used, Year of construction: 2011, functionality: fully functional, machine/vehicle number: 106546-11, total height: 3,550 mm, total length: 7,185 mm, total width: 4,720 mm, overall weight: 8,000 kg, The drilling method used by the deep hole drilling machine is single-lip gun drilling. Drilling Unit Information: - Number of spindles: 1 - Spindle speed, infinitely variable: 500 - 8,000 rpm - Spindle drive power: 11 kW at 60% duty cycle - Max. drilling depth: 1,000 mm (in one pass, no retraction required) - Drilling diameter: 3 - 35 mm (based on ST 60) - Drilling diameter / indexable inserts: 40 mm - Max. thread cutting: M27 - Milling material removal rate: 250 ccm/min Travel Paths: - X-axis travel: 1,050 mm - Y-axis travel: 600 mm - Z-axis travel: 800 mm - W-axis travel: 1,250 mm (with 2 steadies) Caodpfx Afsxdm Awolja Traverse Speeds: - X-axis speed: 15,000 mm/min - Y-axis speed: 15,000 mm/min - Z-axis speed: 15,000 mm/min - W-axis speed: 15,000 mm/min Fluid System Information: - Coolant supply: deep drilling oil - Tank capacity: 1,200 liters - 1 x scraper-belt chip conveyor - 1 x screw conveyor system - 1 x hydraulic unit and pneumatic unit/equipment - 1 x central lubrication system - 1 x submersible pump: Pump delivery: 200 l/min - 1 x low-pressure pump: Pump delivery: 100 l/min Drive power: 2.2 kW - 1 x compact band filter: Filtration rate: 175 l/min For machining steel and non-ferrous metals - 1 x radial piston pump with remote adjustment: Delivery rate: 2 - 120 l/min Pump drive: 11 kW - 1 x air cooler (heat exchanger): 22.5 kW - 1 x oil mist extraction unit: Extraction capacity: 1,250 m³/h Milling and Drilling Spindle Unit: - For conventional machining - Spindle head with tool holder SK 40 Tool Changer Magazine comprising: - Tool magazine with intermediate gripper - Tool holder SK 40 - Max. permitted tool diameter: 80 mm - Max. permitted tool length: 250 mm - Number of tool storage positions: 80 - 2 x swiveling tool steady rests for guiding and supporting long drilling tools, with automatic positioning to home position. Clamping Table with B-Axis and NC Rotary Table: - Length / width: 800 x 600 mm - B-axis: 360° - Positioning accuracy, B-axis: +/- 30 seconds - Table travel: 800 mm - Payload (centered): 1,500 daN Electrical Equipment Information: - 1 x CNC control system, Heidenhain iTNC 530 - 1 x drilling process monitoring - 1 x RENISHAW touch probe Connection Data: - Operating voltage: 3AC 400V ± 10% - Frequency: 50 Hz - Control voltage: 24 V DC - Total connected load: 26 kW

Condition: used, Year of construction: 1973, Tires up to 21 inches Cedpfx Aexcmhkeflsaa