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Hex Bits

Hex Bits

Hex driver bits engage the internal-hex (Allen) recess on socket cap screws, button head sockets, countersunk sockets, grub screws and machine screws. The bit AF (across flats) dimension must match the recess AF exactly - 0.1mm undersize is enough to round out the socket on an installation tighten.

Also known as: Allen Bits, Hex Insert Bits, Hex Power Bits, HX Bits, Hex Drive Bits, Internal Hex Bits.

Hex drive transfers torque on six flat surfaces inside the recess, which gives high torque capacity with very little cam-out tendency. The trade-off: rounded recesses are hard to recover (the bit just spins in the worn hex). Match the bit size precisely; if the bit slides into the recess with any rotational play, it's the wrong size.

GRADES AND MATERIALS

Alloy Tool Steel is the standard Hex bits material. Heat-treated to a hardness around 60 HRC at the tip for wear resistance, with a slightly softer shank to absorb torsional shock. Most bits are supplied with a bright finish. Alpha (Sheffield Group) bits are the workhorse stock here; Sutton Tools and Hobson Engineering carry equivalent grades.

Alloy Tool Steel, Black Finish is the impact-rated variant - tempering profile tuned for higher fatigue resistance under impact-driver blows. Use these on Hex bits that see constant cordless-impact work. Bright-finish bits in an impact driver will snap at the hex shank after 50 to 200 blows.

DRIVE AND INSTALLATION

Insert the bit into a 1/4" hex chuck or a magnetic bit holder. Verify the bit tip matches the fastener recess exactly - undersized bits cam out and strip the recess on the first install. Apply firm axial pressure during driving so the bit stays fully seated. For high-volume work, use power-length bits (50mm+) with a torsion zone to absorb impact-driver hammer blows.

Bit AF runs 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm, 6mm, 8mm, 10mm in metric and 1/16" to 3/8" in imperial. The screw recess size matches the bit AF (e.g. an M6 Socket Cap Screw takes a 5mm hex bit). Imperial and metric hex sizes are NOT interchangeable - 5mm hex is NOT 3/16". For Post Hex security sockets, use the dedicated security bit with a centre hole.

A NOTE ON BIT WEAR AND CAM-OUT

Hex bits are wear items. Match the bit to the fastener recess exactly, lean into the drive so the bit stays fully seated, and replace bits at the first sign of tip rounding. Cam-out (bit slipping out of the recess under torque) is the failure mode - it strips the fastener recess and wears the bit tip simultaneously. If you're seeing cam-out, the bit is either wrong-size or worn.

SIZING AND LENGTHS

Sized by hex AF dimension - the same dimension as the fastener recess. Length options: 25mm insert, 50mm to 90mm power-length. The longer power lengths reach into recessed socket cap installations (through deep counterbores in machinery housings).

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Hex driver bits engage the internal-hex (Allen) recess on socket cap screws, button head sockets, countersunk sockets, grub screws and machine screws. The bit AF (across flats) dimension must match the recess AF exactly - 0.

TECHNICAL RESOURCES

Standard: ISO 4753 (hex drive dimensions, screws). Hex bit AF dimensions match the published socket-cap screw recess for each thread size - see the Sockets category for the matching screws. Spec sheets and dimensional drawings linked on each individual product page. Alpha (Sheffield Group) is a Hobson Engineering supply partner; full Alpha catalogue is on the Sheffield Group website.

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