4-8 NPSL NPSL (straight, locknut) External Thread Specifications

4-8 NPSL · 4.000-8 NPSL

ASMESTD: ASME B1.20.1SOURCE: Table 7 · p. 18TYPE: External (bolt/screw)CLASS: —SERIES: NPSL (straight, locknut)STRAIGHT

Major diameter

4.502 – —

max – min, at the gage plane

Pitch diameter

4.4184 – 4.4067

max – min, at the gage plane

Minor diameter

4.3351 – —

max – min, at the gage plane

Pitch

0.12500

8 threads per inch

Thread profile

External profile over three pitches at the gage plane, drawn at maximum material (sharpest crest, flattest root); hatched bands are the truncation zones. Diameters shortened.

Limits of size, class —

Dimension	Basic	Max	Min	Tolerance
Major diameter D1Crest of the external thread		4.502	—	—
Pitch diameter E1Straight thread: the limits apply along the whole length	4.38713	4.4184	4.4067	0.0117
Minor diameter K1Root of the external thread		4.3351ref.	—	—
Allowance esTable 7 Note 1: allowance equal to the increase in PD per turn, 0.0625/n		0.00781
Crest truncation fcTable 1 (both threads)		0.012500	0.012500
Root truncation frTable 1 (both threads)		0.012500	0.012500
Crest flat FcEquivalent width of flat		0.014434	0.014434
Root flat FrEquivalent width of flat		0.014434	0.014434

Dimensions in inches. Values are those of the standard (ASME B1.20.1); calculated cells follow the standard’s formulas. Where the standard prints a value that differs from its formula, the printed value is shown with a note.

Taper, lengths and gaging

Taper, gage and sealing paras. 3, 5; Tables 1, 3

Taper on the diameter T: none (straight)
Half apex angle of the pitch cone β: 0 °
Lead angle at the basic PD λ: 0° 31′
Gaging method: GO / NOT GO thread gages or indicating gages to ASME B1.2 (para. 6.4); NOT GO may enter up to 3 turns
Gaging tolerance: limits of size (tolerance equals 1.5 turns, Table 7 Note 1)
Gaging position: not applicable (straight thread)
Sealing: Mechanical joint, no sealing requirement (section 6)

Notes

Table 7 Note 1: major and minor diameters vary with PD (single-point form). External max major = max PD + 0.666025P (truncated depth); commercial pipe may not reach it. An allowance equal to the PD increase per turn is provided, with a tolerance of 1.5 turns for both threads. Gages: GO / NOT GO to the PD limits of Table 7 per ASME B1.2 (para. 6.4.4).

Mates

4-8 NPSL screws into a thread of the same standard at the same size and pitch. The standard mating internal thread is class Std. Check the fit with the standard pair →

Working out the mating options…

Different pitch or a different thread family never mate; the fit check runs over both tolerance zones.

Related thread sizes

Same diameter other pitch, and neighbouring sizes

→ 4-8 NPT → 4-8 NPTR → 4-8 NPSM → 3-1/2-8 NPSL → 5-8 NPSL → 4-8 NPSL internal

All values for 4-8 NPSLevery column of the workbook row

All values of the workbook row 4-8 NPSL
Designation	4-8 NPSL
Decimal designation	4.000-8 NPSL
Threads per inch	8
Thread form	Straight
Series	NPSL
Series name	Straight Pipe Threads for Loose-fitting Mechanical Joints with Locknuts
External / internal	External
Class	—
Nominal pipe size	4
Pitch P (in.)	0.12500000
O.D. of pipe D, basic major dia (in.)	4.500
Size category (Table 3 group)	2-1/2 and larger (8 TPI)
Source table	Table 7
Printed page	18
Where the diameter limits apply	Straight thread: the limits apply along the whole length
Major dia max (in.)	4.502
Major dia status	Max only (Table 7 col. 4, Note 1: theoretical; commercial pipe may not have it); min not given in the standard
Basic pitch dia at gage plane E1 (in.)	4.38713
Pitch dia max (in.)	4.4184
Pitch dia min (in.)	4.4067
PD tolerance (in.)	0.0117
Minor dia max (in.)	4.3351
Minor dia status	Not given in the standard; reference max = PD max − 0.666025P (Note 1)
Allowance (in.)	0.00781
Allowance source	Table 7 Note 1: allowance equal to the increase in PD per turn, 0.0625/n
Root radius max (in.)	not given in the standard
Root radius min (in.)	not given in the standard
Lead / angle / taper source	Not given in the standard for straight threads
Lead angle at basic PD (deg)	0.519625
Lead angle (deg min)	0° 31′
Tensile stress area As (sq in.)	not given in the standard
Thread angle (deg)	60
Flank angle (deg)	30
Sharp V height H (in.)	0.1082532
Thread height h max (in.)	0.083253
Thread height h min (in.)	0.083253
Crest truncation min (in.)	0.012500
Crest truncation max (in.)	0.012500
Root truncation min (in.)	0.012500
Root truncation max (in.)	0.012500
Crest flat min (in.)	0.014434
Crest flat max (in.)	0.014434
Root flat min (in.)	0.014434
Root flat max (in.)	0.014434
Sweep cut: start diameter (in.)	4.502
Sweep cut: tip diameter (in.)	4.335494
Sweep cut: depth (in.)	0.083253
Sweep cut: profile width at start diameter (in.)	0.110566
Sweep cut: tip flat (in.)	0.014434
Sweep cut: start diameter is	Major dia max (cylinder)
Taper half-angle β (deg)	0
Taper on diameter	none (straight)
Gaging method	GO / NOT GO thread gages or indicating gages to ASME B1.2 (para. 6.4); NOT GO may enter up to 3 turns
Gaging tolerance (turns)	limits of size (tolerance equals 1.5 turns, Table 7 Note 1)
Basic gaging position	not applicable (straight thread)
Sealing	Mechanical joint, no sealing requirement (section 6)
Major dia max by formula (ext)	4.502
Check against formulas	OK
Notes	Table 7 Note 1: major and minor diameters vary with PD (single-point form). External max major = max PD + 0.666025P (truncated depth); commercial pipe may not reach it. An allowance equal to the PD increase per turn is provided, with a tolerance of 1.5 turns for both threads. Gages: GO / NOT GO to the PD limits of Table 7 per ASME B1.2 (para. 6.4.4).
Lookup key	4-8 NPSL · External

ASME B1.20.1: Pipe Threads, General Purpose, Inch. Source: workbook data (2026-10-11). Confirm against your licensed copy of the standard before use.

4-8 NPSL NPSL (straight, locknut) External Thread Specifications

Thread profile

Limits of size, class —

Taper, lengths and gaging

Taper, gage and sealing paras. 3, 5; Tables 1, 3

Notes

Mates

Related thread sizes

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