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).
M33 × 3.5 in numbers
M33 × 3.5 is 33 mm across the crests with a 3.5 mm pitch, which is 7.3 threads per inch. The basic pitch diameter is 30.727 mm and the bolt's minor diameter 28.706 mm, so the thread is 2.147 mm deep on the bolt. The nearest inch size, 1-1/4-7 UNC, is 1.25 mm smaller across the crests and its pitch is 0.129 mm coarser, so the two do not interchange.
Tap drill by thread percentage
Hole = D − % × 0.0129904 × P, with D = 33 mm and P = 3.5 mm. A smaller hole leaves more thread; the recommended 29.5 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 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 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 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 2061 N·m (Class 8.8) to 3332 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.