M8 Hex Head Bolt, Fully Threaded are manufactured to GB/T 5783 / ISO 4017 with a coarse thread pitch of 1.25 mm. This page lists the controlling dimensions for the M8 size — head geometry, width across flats, matching spanner size — together with the clearance hole, tapping drill and tightening torque used at assembly.
M8 Dimensional Row (GB/T 5783 / ISO 4017)
| Size | Pitch (mm) | Nominal diameter d (mm) | Length L (mm) | Width across flats s (mm) | Width across corners e (mm) | Head height k (mm) |
|---|---|---|---|---|---|---|
| M8 | 1.25 | 8 | 50 | 13.0 | 14.38 | 5.3 |
Spanner & Drive for M8 Hex Head Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 012)
M8 Hex Head Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 012) have a width across flats of 13.0 mm — fit a 13.0 mm open-ended spanner or socket. Use a 6-point socket for tight clearances and to reduce rounding; for repeated assembly choose a torque wrench so the joint preload is repeatable.
Hole Sizes for M8
| Coarse-thread pitch (ISO 724) | 1.25 mm |
|---|---|
| Through-hole / clearance (ISO 273 medium) | 9 mm |
| Tapping drill, coarse thread | 6.8 mm |
Tightening Torque for M8
| Class 8.8 (dry, ~µ 0.125) | ≈ 25 Nm |
|---|---|
| Class 10.9 (dry, ~µ 0.125) | ≈ 35 Nm |
| Class 12.9 (dry, ~µ 0.125) | ≈ 41 Nm |
Indicative dry-joint values. Lubrication can lower the required torque by 15–25%. Always confirm against the joint design, especially when going up a strength class.
Proof Load & Strength for M8
| Tensile stress area As (ISO 898-1) | 36.6 mm² |
|---|---|
| Proof load, class 8.8 | 21 kN |
| Proof load, class 10.9 | 30 kN |
| Proof load, class 12.9 | 36 kN |
| Min. ultimate tensile, class 8.8 | 29 kN |
Proof load = stress area × proof stress per ISO 898-1. Design joints so the working preload stays below the proof load of the selected class.
M8 Hex Head Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 012) Weight
A steel M8 hex head bolt, fully threaded at the listed 50 mm length weighs approximately 26 g each — about 26 kg per 1,000 pieces. Stainless A2/A4 weighs roughly the same (density 7.9–8.0 g/cm³). Actual weight varies slightly with head form, thread and finish; use this figure for freight estimation only.
Common Applications for M8 Hex Head Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 012)
M8 Hex Head Bolt, Fully Threaded — GB/T 5783 / ISO 4017 (Series 012) are commonly specified for general-purpose machinery, jigs, fixturing and light structural connections.
Mating Parts for M8
For M8, pair with a M8 hex nut (ISO 4032 / DIN 934) and, where used, a M8 flat washer (ISO 7089 / DIN 125A) under the head and under the nut.
When to Step Up or Down from M8
When the joint preload approaches the proof load of M8 class 8.8, step up to M10 class 8.8 (or move to M8 class 10.9). When the joint is over-specified, M6 often saves weight and cost without losing the safety margin.