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).
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 M33 × 3.5 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 M33 × 3.5?
For a M33 × 3.5 thread, drill the hole with a 29.5 mm tap drill (29.5 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 33 mm and a pitch of 3.5 mm (≈7.26 TPI (converted)).
To pass a M33 × 3.5 bolt through a part rather than thread it, use a clearance hole: Close 34 · Normal 36 · Loose 38 mm.
All values are generated from the standard thread formulas (ISO 68-1 / ASME B1.1) and published standard tables - not hand-entered. See the full reference.
Frequently asked questions
What drill size do I need to tap a M33 × 3.5 thread?
Drill 29.5 mm before tapping M33 × 3.5. That leaves roughly 77% thread engagement, the usual target for a strong hole that still taps cleanly.
Is M33 × 3.5 a coarse or fine thread?
M33 × 3.5 is a metric coarse thread. Coarse is the default pitch for M33: when a drawing or supplier says just M33, it means this 3.5 mm pitch.
What size clearance hole does a M33 × 3.5 bolt need?
Drill 34 mm for a close fit, 36 mm for a normal fit or 38 mm for a loose fit (ISO 273). A clearance hole lets the M33 × 3.5 bolt pass through the part instead of threading into it.
How much torque should I use on a M33 × 3.5 bolt?
Estimated tightening torque for M33 × 3.5 runs from 2059.9 N·m (Class 8.8) to 3330.1 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.