M42×2 Thread Dimensions and Tap Drill

M42×2 is an ISO metric fine-pitch thread: the 42 mm diameter with a 2 mm pitch (12.7 threads per inch) instead of the coarse 4.5 mm of M42×4.5. The thread is 1.35 mm shallower, so the tensile stress area rises from 1120 to 1260 mm² (13% more) and the lead angle falls from 2.10° to 0.90°.

Tap drill40 mm77% thread
Pitch2 mm12.7 TPI
Major diameter42.000 mm1.6535 in
Pitch diameter40.701 mm1.6024 in
Minor diameter (nut)39.835 mm1.5683 in
Tensile stress area1260 mm²1.96 in²
Clearance hole45 mmmedium fit, ISO 273

Thread profile

M42×2 drawn to scale: 48 threads in 96.2 mm of length.

Basic profile with the M42×2 dimensions. The nut and bolt share the same pitch diameter.

M42×2 basic dimensions

Dimension	mm	in
Major diameter d = D	42.000	1.6535
Pitch P	2.000	0.0787
Pitch diameter d₂ = D₂	40.701	1.6024
Minor diameter, internal thread D₁	39.835	1.5683
Minor diameter, external thread d₃	39.546	1.5569
Height of fundamental triangle H	1.732	0.0682
Thread height, internal (5H/8)	1.083	0.0426
Thread height, external (17H/24)	1.227	0.0483
Crest flat of external thread (P/8)	0.250	0.0098
Crest flat of internal thread (P/4)	0.500	0.0197

Property	Value
Threads per inch	12.70
Flank angle	60° (30° each side)
Lead angle at the pitch diameter	0.90°
Tensile stress area A_s	1260 mm² (1.96 in²)

Basic (nominal) sizes per ISO 724, before tolerances. d₃ is the root diameter of a bolt with the rounded root that ISO 898-1 uses for the stress area.

M42×2 tolerance limits (6g bolt, 6H nut)

6g and 6H are the general-purpose tolerance classes for commercial screws and nuts. The 6g screw has a fundamental deviation of 38 µm, so even at its largest it sits 0.038 mm below the basic size and leaves room for a thin plating.

External thread 6g	Max (mm)	Min (mm)	Tolerance (mm)
Major diameter d	41.962	41.682	0.280
Pitch diameter d₂	40.663	40.493	0.170

Internal thread 6H	Max (mm)	Min (mm)	Tolerance (mm)
Minor diameter D₁	40.210	39.835	0.375
Pitch diameter D₂	40.925	40.701	0.224

Computed from the ISO 965-1 deviations and tolerances for normal length of engagement; the results match the limits tabulated in ISO 965-2.

M42×2 tap drill size

Tap drill for M42×2: 40 mm

This leaves about 77% thread in the tapped hole.

The rule for metric tap drills is diameter minus pitch: 42 − 2 = 40 mm, which is a stocked drill size.

The 6H minor diameter of the finished nut thread must lie between 39.835 and 40.210 mm. The recommended drill falls inside that band.

Other drills that work for M42×2

A larger drill cuts less thread and taps more easily; a smaller one gives a fuller thread but loads the tap harder.

Drill	mm	in	% thread	Within 6H limits
40 mmrecommended	40.00	1.5748	77%	yes
1-37/64" (1.5781 in)	40.08	1.5781	74%	yes
40.5 mm	40.50	1.5945	58%	no

% thread = (major diameter − drill diameter) ÷ (1.299 × pitch). See the tap drill chart for how to choose a percentage.

Clearance hole for M42

The clearance hole depends only on the 42 mm diameter, not on the pitch. The medium series, 45 mm, is the usual choice for general assembly.

Series	Hole Ø (mm)	Hole Ø (in)	Clearance on Ø (mm)
Fine (H12)	43	1.6929	1
Medium (H13)	45	1.7717	3
Coarse (H14)	48	1.8898	6

Hole diameters from ISO 273.

M42×2 strength

ISO 898-1 tabulates fine-pitch loads only for a selected set of threads from M8×1 to M39×3, so it gives no proof or breaking loads for M42×2. For an estimate, multiply the tensile stress area of 1260 mm² by the stress of the material: for example, 800 MPa gives 1010 kN.

M42 pitches compared

All standard pitches on the M42 diameter. A finer pitch gives a shallower thread, a larger core and a smaller lead angle; a coarser pitch is faster to assemble and more tolerant of damage and plating.

M42 pitches at the same scale with crests aligned; M42×2 is outlined.

Thread	Pitch (mm)	Pitch Ø (mm)	Minor Ø D1 (mm)	Stress area (mm²)	Tap drill
M42×4.5	4.5	39.077	37.129	1120	37.5 mm
M42×3	3	40.051	38.752	1210	39 mm
M42×2	2	40.701	39.835	1260	40 mm
M42×1.5	1.5	41.026	40.376	1290	40.5 mm

When to choose a coarse or a fine thread

Closest inch thread

No inch thread is interchangeable with M42×2. The nearest is 1-5/8-18 UNEF, which is 0.73 mm smaller in diameter with a pitch of 1.411 mm against 2.000 mm. A nut may start on the wrong thread and then bind or strip, so identify by both diameter and pitch.

Thread	Major Ø (mm)	Pitch (mm)	TPI	Ø difference (mm)
M42×2 (this thread)	42.000	2.000	12.70	—
1-5/8-18 UNEF	41.275	1.411	18.00	-0.725
1-11/16-18 UNEF	42.862	1.411	18.00	+0.862
1-9/16-18 UNEF	39.688	1.411	18.00	-2.312

Identify a thread from measurements

How the M42×2 dimensions are calculated

Every basic dimension follows from the major diameter and the pitch:

P = 2 mm
H = 0.866025 × P = 1.732 mm
d₂ = d − 0.649519 × P = 42 − 1.299 = 40.701 mm
D₁ = d − 1.082532 × P = 42 − 2.165 = 39.835 mm
d₃ = d − 1.226869 × P = 42 − 2.454 = 39.546 mm (external root, 17H/24 deep)
A_s = π/4 × ((d₂ + d₃) ÷ 2)² = π/4 × 40.124² = 1264.42 mm²
Lead angle = arctan(P ÷ (π × d₂)) = 0.90°

Related sizes and tools

Sources: ISO 68-1 and ISO 724 (profile and basic dimensions), ISO 261 (diameter and pitch series), ISO 965-1 (tolerances), ISO 273 (clearance holes), ISO 898-1 (mechanical properties) and tap drill tables based on ISO 2306. How this site checks its data. Last reviewed 29 September 2026.