Unified Threads Gauges for testing Unified threads to BS 1580: Parts 1&2:2007, BS 1580: Part 3: 2007, and BS 919: Part 1: 2007 BS 1580: Pt1: 2007 specifies details of product threads. The standard includes nominal sizes and limits of size for standard threads for 1A, 2A and 3A for external threads, and 1B, 2B and 3B for internal threads in the following sizes: UNC (coarse pitch) from ¼" to 4" dia. UNF (fine pitch) from ¼" to 1½" dia. UNEF (extra fine pitch) from ¼" to 1 11/16" dia. UN (constant pitch) for 4, 6, 8, 12, 16, 20, 28 and 32 tpi for various diameters as specified. Allowances (deviation from basic size) 1A and 2A provide allowances of 30% of the effective diameter tolerances of 2A external threads. 3A is basic (no allowance). 2AG is 0.001" smaller on diameter to provide for plating to finish at 2A . (0.001” on diameter will allow for an average deposit of 0.00025”). 1B, 2B and 3B for internal threads are all basic. Before plating, threads are not designated. They are referred to as before plating and are 0.001” larger on diameter than basic size.

1224NGR UNC No Go Ring Gauges Description : Thread ring gauge No Go Size & TPI : 12 X 24 Class : 2A To BS 1580 Tolerance to BS 919 Blanks to BS 1044