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).
M42 × 3.0 in numbers
M42 × 3.0 is 42 mm across the crests with a 3 mm pitch, which is 8.5 threads per inch. The basic pitch diameter is 40.052 mm and the bolt's minor diameter 38.319 mm, so the thread is 1.84 mm deep on the bolt. Its tensile stress area is 1206 mm², 8% more than the coarser M42 × 4.5 at the same diameter. The nearest inch size, 1-3/4-5 UNC, is 2.45 mm larger across the crests and its pitch is 2.080 mm coarser, so the two do not interchange.
Tap drill by thread percentage
Hole = D − % × 0.0129904 × P, with D = 42 mm and P = 3 mm. A smaller hole leaves more thread; the recommended 39 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. ISO 898-1's tabulated range stops at M39; above that the same class values apply only by agreement between supplier and purchaser.
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 M42 × 3.0 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 M42 × 3.0?
For a M42 × 3.0 thread, drill the hole with a 39 mm tap drill (39 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 42 mm and a pitch of 3 mm (≈8.47 TPI (converted)).
To pass a M42 × 3.0 bolt through a part rather than thread it, use a clearance hole: Close 43 · Normal 45 · Loose 48 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 M42 × 3.0 thread?
Drill 39 mm before tapping M42 × 3.0. That leaves roughly 77% thread engagement, the usual target for a strong hole that still taps cleanly.
Is M42 × 3.0 a coarse or fine thread?
M42 × 3.0 is a metric fine thread. Its 3 mm pitch is tighter than the standard coarse pitch for M42, which suits thin walls, fine adjustment and vibration-sensitive joints.
What size clearance hole does a M42 × 3.0 bolt need?
Drill 43 mm for a close fit, 45 mm for a normal fit or 48 mm for a loose fit (ISO 273). A clearance hole lets the M42 × 3.0 bolt pass through the part instead of threading into it.
How much torque should I use on a M42 × 3.0 bolt?
Estimated tightening torque for M42 × 3.0 runs from 4559 N·m (Class 8.8) to 7370 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.