M45×2 Thread Dimensions and Tap Drill

M45×2 is an ISO metric fine-pitch thread: the 45 mm diameter with a 2 mm pitch (12.7 threads per inch) instead of the coarse 4.5 mm of M45×4.5. The thread is 1.35 mm shallower, so the tensile stress area rises from 1310 to 1460 mm² (12% more) and the lead angle falls from 1.95° to 0.83°.

Tap drill43 mm77% thread
Pitch2 mm12.7 TPI
Major diameter45.000 mm1.7717 in
Pitch diameter43.701 mm1.7205 in
Minor diameter (nut)42.835 mm1.6864 in
Tensile stress area1460 mm²2.26 in²
Clearance hole48 mmmedium fit, ISO 273

Thread profile

M45×2 drawn to scale: 52 threads in 103.1 mm of length.

Basic profile with the M45×2 dimensions. The nut and bolt share the same pitch diameter.

M45×2 basic dimensions

Dimension	mm	in
Major diameter d = D	45.000	1.7717
Pitch P	2.000	0.0787
Pitch diameter d₂ = D₂	43.701	1.7205
Minor diameter, internal thread D₁	42.835	1.6864
Minor diameter, external thread d₃	42.546	1.6750
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	0.83°
Tensile stress area A_s	1460 mm² (2.26 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.

M45×2 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	44.962	44.682	0.280
Pitch diameter d₂	43.663	43.493	0.170

Internal thread 6H	Max (mm)	Min (mm)	Tolerance (mm)
Minor diameter D₁	43.210	42.835	0.375
Pitch diameter D₂	43.925	43.701	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.

M45×2 tap drill size

Tap drill for M45×2: 43 mm

This leaves about 77% thread in the tapped hole.

The rule for metric tap drills is diameter minus pitch: 45 − 2 = 43 mm, which is a stocked drill size.

The 6H minor diameter of the finished nut thread must lie between 42.835 and 43.210 mm. The recommended drill falls inside that band.

Other drills that work for M45×2

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
1-11/16" (1.6875 in)	42.86	1.6875	82%	yes
43 mmrecommended	43.00	1.6929	77%	yes
43.5 mm	43.50	1.7126	58%	no

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

Clearance hole for M45

The clearance hole depends only on the 45 mm diameter, not on the pitch. The medium series, 48 mm, is the usual choice for general assembly.

Series	Hole Ø (mm)	Hole Ø (in)	Clearance on Ø (mm)
Fine (H12)	46	1.8110	1
Medium (H13)	48	1.8898	3
Coarse (H14)	52	2.0472	7

Hole diameters from ISO 273.

M45×2 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 M45×2. For an estimate, multiply the tensile stress area of 1460 mm² by the stress of the material: for example, 800 MPa gives 1170 kN.

M45 pitches compared

All standard pitches on the M45 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.

M45 pitches at the same scale with crests aligned; M45×2 is outlined.

Thread	Pitch (mm)	Pitch Ø (mm)	Minor Ø D1 (mm)	Stress area (mm²)	Tap drill
M45×4.5	4.5	42.077	40.129	1310	40.5 mm
M45×3	3	43.051	41.752	1400	42 mm
M45×2	2	43.701	42.835	1460	43 mm
M45×1.5	1.5	44.026	43.376	1490	43.5 mm

When to choose a coarse or a fine thread

Closest inch thread

No inch thread is interchangeable with M45×2. The nearest is 1-11/16-18 UNEF, which is 2.14 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)
M45×2 (this thread)	45.000	2.000	12.70	—
1-11/16-18 UNEF	42.862	1.411	18.00	-2.138
1-3/4-5 UNC	44.450	5.080	5.00	-0.550

Identify a thread from measurements

How the M45×2 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 = 45 − 1.299 = 43.701 mm
D₁ = d − 1.082532 × P = 45 − 2.165 = 42.835 mm
d₃ = d − 1.226869 × P = 45 − 2.454 = 42.546 mm (external root, 17H/24 deep)
A_s = π/4 × ((d₂ + d₃) ÷ 2)² = π/4 × 43.124² = 1460.56 mm²
Lead angle = arctan(P ÷ (π × d₂)) = 0.83°

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.