#4-48 UNF Thread Dimensions and Tap Drill
#4-48 UNF is the Unified fine thread for the number 4 size (major diameter 0.112 in, 2.84 mm): 48 threads per inch, a pitch of 0.02083 in (0.529 mm), on a 60° profile. ASME B1.1 lists it in the UNF series. Against the coarse #4-40 UNC it has 48 threads per inch instead of 40, a stress area 9% larger and a lead angle of 3.85° instead of 4.75°.
- Tap drill#4268% thread, 2.37 mm
- Pitch48 TPI0.529 mm
- Major diameter0.1120 in2.845 mm
- Pitch diameter0.0985 in2.501 mm
- Minor diameter (nut)0.0894 in2.272 mm
- Tensile stress area0.00661 in²4.26 mm²
- Clearance hole#30normal fit, ASME B18.2.8
Thread profile
#4-48 UNF basic dimensions
| Dimension | in | mm |
|---|---|---|
| Major diameter d = D | 0.1120 | 2.845 |
| Pitch P | 0.02083 | 0.529 |
| Pitch diameter d2 = D2 | 0.0985 | 2.501 |
| Minor diameter, internal thread D1 | 0.0894 | 2.272 |
| Minor diameter, external UNR thread d3 | 0.0872 | 2.215 |
| Height of fundamental triangle H | 0.0180 | 0.458 |
| Thread height, internal (5H/8) | 0.0113 | 0.286 |
| Thread height, external (11H/16) | 0.0124 | 0.315 |
| Crest flat of external thread (P/8) | 0.0026 | 0.066 |
| Crest flat of internal thread (P/4) | 0.0052 | 0.132 |
| Property | Value |
|---|---|
| Threads per inch | 48 |
| Flank angle | 60° (30° each side) |
| Lead angle at the pitch diameter | 3.85° |
| Tensile stress area As | 0.00661 in² (4.26 mm²) |
Basic (nominal) sizes per ASME B1.1, before tolerances. A UN external thread with a flat root has the same basic minor diameter as the nut (D1); d3 applies to the rounded UNR root.
#4-48 UNF limits of size (class 2A bolt, 2B nut)
Classes 2A and 2B are the general-purpose fits for commercial bolts, screws and nuts. The 2A external thread has an allowance of 0.0007 in, so its maximum size is that much below basic; the 2B nut starts at the basic size.
| External thread 2A | Max (in) | Min (in) | Tolerance (in) |
|---|---|---|---|
| Major diameter | 0.1113 | 0.1068 | 0.0045 |
| Pitch diameter | 0.0978 | 0.0954 | 0.0024 |
| Internal thread 2B | Max (in) | Min (in) | Tolerance (in) |
|---|---|---|---|
| Minor diameter | 0.0968 | 0.0894 | 0.0074 |
| Pitch diameter | 0.1016 | 0.0985 | 0.0031 |
Limits of size from ASME B1.1 Table 2.
#4-48 UNF tap drill size
Tap drill for #4-48 UNF: #42 (0.0935 in, 2.37 mm)
This leaves about 68% thread in the tapped hole.
#42 is the drill listed for #4-48 UNF in standard tap drill charts. It is 0.0185 in under the 0.1120 in major diameter.
The 2B minor diameter of the finished nut thread must lie between 0.089 and 0.097 in. The recommended drill falls inside that band.
Other drills that work for #4-48 UNF
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 2B limits | Thread engagement |
|---|---|---|---|---|---|
| #43 | 2.26 | 0.0890 | 85% | no | |
| 2.35 mm | 2.35 | 0.0925 | 72% | yes | |
| #42recommended | 2.37 | 0.0935 | 68% | yes | |
| 3/32" | 2.38 | 0.0938 | 67% | yes | |
| #41 | 2.44 | 0.0960 | 59% | yes | |
| #40 | 2.49 | 0.0980 | 52% | no |
% thread = (major diameter − drill diameter) ÷ (1.299 × pitch). See the tap drill chart for how to choose a percentage.
Clearance hole for #4
The clearance hole depends only on the 0.1120 in diameter, not on the thread series. The normal fit, a #30 drill, is the usual choice for general assembly.
| Fit | Drill | Hole Ø (in) | Hole Ø (mm) | Clearance on Ø (in) |
|---|---|---|---|---|
| Close | #31 | 0.1200 | 3.05 | 0.0080 |
| Normal | #30 | 0.1285 | 3.26 | 0.0165 |
| Loose | #27 | 0.1440 | 3.66 | 0.0320 |
Nominal drill sizes from ASME B18.2.8.
#4-48 UNF strength
SAE J429 starts at 1/4 in, so the SAE grades give no proof load for #4-48 UNF. For an estimate, multiply the tensile stress area of 0.00661 in² by the strength of the material: for example, 60,000 psi gives 397 lbf.
#4 pitches compared
All standard pitches on the #4 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.
| Thread | TPI | Pitch Ø (in) | Minor Ø D1 (in) | Stress area (in²) | Tap drill |
|---|---|---|---|---|---|
| #4-40 UNC | 40 | 0.0958 | 0.0849 | 0.00604 | #43 |
| #4-48 UNF | 48 | 0.0985 | 0.0894 | 0.00661 | #42 |
Closest metric thread
No metric thread is interchangeable with #4-48 UNF. The nearest is M3×0.5, which is 0.16 mm larger in diameter with a pitch of 0.500 mm against 0.529 mm. A nut may start on the wrong thread and then bind or strip, so identify by both diameter and pitch.
How the #4-48 UNF dimensions are calculated
Every basic dimension follows from the major diameter and the pitch:
- P = 0.02083 in = 1 ÷ 48 threads per inch
- H = 0.866025 × P = 0.0180 in
- d2 = d − 0.649519 × P = 0.1120 − 0.0135 = 0.0985 in
- D1 = d − 1.082532 × P = 0.1120 − 0.0226 = 0.0894 in
- d3 = d − 1.190785 × P = 0.1120 − 0.0248 = 0.0872 in (external root, 11H/16 deep)
- As = 0.7854 × (d − 0.9743 × P)² = 0.7854 × 0.0917² = 0.00660 in²
- Lead angle = arctan(P ÷ (π × d2)) = 3.85°
Related sizes and tools
Sources: ASME B1.1 (profile, series, limits of size and stress area), ASME B18.2.8 (clearance holes), SAE J429 (mechanical properties) and the tap drill tables of Machinery’s Handbook. How this site checks its data. Last reviewed 29 September 2026.