Dimensions
Wrench sizes follow ISO 4014 / ISO 4017. Older DIN 931 / DIN 933 bolts differ at several sizes (M10 = 17, M12 = 19, M14 = 22, M22 = 32) - check the bolt before choosing a spanner.
ISO 273 clearance holes (fine / medium / coarse).
M8 × 0.75 in numbers
M8 × 0.75 is 8 mm across the crests with a 0.75 mm pitch, which is 33.9 threads per inch. The basic pitch diameter is 7.513 mm and the bolt's minor diameter 7.08 mm, so the thread is 0.46 mm deep on the bolt. Its tensile stress area is 41.8 mm², 14% more than the coarser M8 × 1.25 at the same diameter. The nearest inch size, 5/16-18 UNC, is 0.06 mm smaller across the crests and its pitch is 0.661 mm coarser, so the two do not interchange.
Tap drill by thread percentage
Hole = D − % × 0.0129904 × P, with D = 8 mm and P = 0.75 mm. A smaller hole leaves more thread; the recommended 7.25 mm drill above gives about 77%.
Tightening torque estimate
Target preload is 75% of proof load; torque is estimated from T = K · F · d.
Strengths are ISO 898-1:2013 Table 3 for d ≤ 16 mm. Class 8.8 is size-banded - 580 MPa proof at or below 16 mm, 600 MPa above - while 10.9 and 12.9 hold one value across the range.
These figures assume a nut factor of K = 0.20 (dry / as-received steel). K captures thread and head friction and can swing torque by 30% or more - a lubricated joint needs noticeably less. Change the lubrication assumption in the bolt-torque calculator. Put M8 × 0.75 on a job sheet
The bolt schedule collects the fasteners for one job onto a single sheet - tap drill, wrench size, grade and tightening torque on every line, taken straight from pages like this one. Free schedules hold 3 lines and are saved in this browser only.
What tap drill do I need for M8 × 0.75?
For a M8 × 0.75 thread, drill the hole with a 7.25 mm tap drill (7.25 mm - the standard D − P rule) before tapping. That produces roughly 77% thread engagement, the usual target for a strong, tappable hole. The mating bolt has a major diameter of 8 mm and a pitch of 0.75 mm (≈33.87 TPI (converted)).
To pass a M8 × 0.75 bolt through a part rather than thread it, use a clearance hole: Close 8.4 · Normal 9 · Loose 10 mm.
All values come from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables. See the full reference.
Frequently asked questions
What drill size do I need to tap a M8 × 0.75 thread?
Drill 7.25 mm before tapping M8 × 0.75. That leaves roughly 77% thread engagement, the usual target for a strong hole that still taps cleanly.
Is M8 × 0.75 a coarse or fine thread?
M8 × 0.75 is a metric fine thread. Its 0.75 mm pitch is tighter than the standard coarse pitch for M8, which suits thin walls, fine adjustment and vibration-sensitive joints.
What size clearance hole does a M8 × 0.75 bolt need?
Drill 8.4 mm for a close fit, 9 mm for a normal fit or 10 mm for a loose fit (ISO 273). A clearance hole lets the M8 × 0.75 bolt pass through the part instead of threading into it.
How much torque should I use on a M8 × 0.75 bolt?
Estimated tightening torque for M8 × 0.75 runs from 29.1 N·m (Class 8.8) to 48.7 N·m (Class 12.9), targeting 75% of proof load with a dry nut factor of K = 0.20. Lubricated threads need noticeably less torque.