Unified Thread Limits Calculator (2A/2B)

Inputs

Nominal major diameter (D)

Threads per inch (TPI)

TPI

Length of engagement

Default result

2A allowance (es)

0.0011 in

0.3 × the 2A PD tolerance — the deliberate clearance class 2A external threads give up (2B starts at basic).

Also computed

2A major dia max (d_max) 0.2489 in

What the blank or thread OD is turned/rolled to.

2A major dia min (d_min) 0.2408 in

2A pitch dia max (d2_max) 0.2164 in

GO limit for the external thread — wires or the ring gauge check this.

2A pitch dia min (d2_min) 0.2127 in

2A PD tolerance 0.0037 in.

2B pitch dia min (D2_min) 0.2175 in

Basic pitch diameter — the internal GO limit.

2B pitch dia max (D2_max) 0.2224 in

2B PD tolerance 0.0049 in (1.3 × the 2A tolerance).

Method notes 4 notes

ASME B1.1 formula method, classes 2A/2B: Td2(2A) = 0.0015·∛D + 0.0015·√LE + 0.015·∛P², allowance = 0.3·Td2(2A), major tolerance 0.060·∛P², Td2(2B) = 1.3·Td2(2A), minor tolerance 0.25P − 0.4P². Values rounded per the standard (tolerances/PD to 0.0001 in, minor limits to 0.001 in) — output matches the published tables.
Classes 1A/3A/1B/3B, UNJ (ASME B1.15) and small number-size special cases are out of scope here; the standard’s own tables govern. UNR differs from UN only in external root radius — these PD/major limits apply to both.
2A maximum major/PD sit one allowance below basic — that clearance is what lets plated or hot assemblies still go together; class 3 fits delete it.
Gauging practice (GO/NOGO, wire methods) is ASME B1.2; the minimum 2B minor is the tap-drill floor, and the thread tap drill size calculator picks the drill.