NPTF TAPER PLUG AND RING GAUGES
NPTF Thread Gauges for testing threads to American National Standard
ASME B1.20.5 - 1991.
This standard provides information on gauges used for testing dryseal threads.
The gauges are intended to be used to test unused pipe threads.
The types of thread designated are NPTF, PTF-SAE SHORT, NPSF and NPSI.
The thread form and taper are the same as for NPT threads.
The pipe fittings range in size from 1/16 inch to 3.0 inch.
NPTF Class 1 and Class 2, and PTF-SAE SHORT threads are tested by the coordinated
use of L1 and L2 ring gauges for external threads, and L1 and L3 plug gauges
for internal threads.
Functions of L1 and L3 Plug gauges
• L1 plugs check the threads when assembled hand tight.
• L3 plugs check the threads when assembled with a wrench.
Functions of L1 and L2 Ring gauges
• L1 rings check the threads when assembled hand tight.
• L2 rings check the threads when assembled with a wrench.
NPSF and NPSI are internal threads, and are tested using the appropriate L1
taper thread plug gauge. These parallel product threads are intended to be
assembled with taper dryseal external threads.
Provision is made for two types of gauge.
| NPTF Screw Plugs | ||
| NPTF L1 | Basic Notch | (1 step) |
| NPTF L1 | Step limit | (4 steps) |
| PTF-SAE short or NPSF L1 | Step limit | (3 step) |
| NPSL1 | Step limit | (3 steps) |
| NPTF L3 | Basic Notch | (1 step) |
| NPTF L3 | Step limit | (4 steps) |
| PTF-SAE SHORT L3 | Step limit | (3 steps) |
| NPTF Screw Rings | ||
| NPTF L1 | Basic Notch | (No step) |
| NPTG L1 | Step limit | (4 steps) |
| PTF-SAE short L2 | Step limit | (3 steps) |
| NPTF L2 | Step limit | (No step) |
| NPTF L2 | Step limit | (4 steps) |
| PTF-SAE SHORT L2 | Step limit | (3 steps) |
Master gauges: used to check new working gauges. Each set
consists of a L1/L3 master ring gauge, and a L1/L2 master plug gauge.
Working gauges: used to check product threads during and
after manufacture. Information on the following types of working gauge is
provided in this standard.
For class 2 threads, crest and root check gauges should also be included in
the set of working gauges. Root check ring and plug gauges have a narrower
thread angle which enables the gauges to contact only at the root of the product
thread, so that the root truncation can be checked. Crest check rings and
plugs are plain taper gauges. Root and crest gauges are used in conjunction
with the 4 step limit gauges.
| Size | NPTF (Dry Seal) ANSI B1.20.5-1991 |
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| L1 Plug | L1 Ring | L3 Plug | L2 Ring | |
| 1/6" | 0510Q | 0574 | 0574 | 0576 |
| 1/8" | 0511Q | 0523 | 0524 | 0525 |
| 1/4" | 0512Q | 0529 | 0530 | 0531 |
| 3/8" | 0513Q | 0534 | 0535 | 0536 |
| 1/2" | 0514Q | 0539 | 0540 | 0541 |
| 3/4" | 0515Q | 0544 | 0545 | 0546 |
| 1" | 01516Q | 0549 | 0550 | 1551 |
| 11/4" | 0517Q | 0554 | 0555 | 0556 |
| 11/2" | 01518Q | 0559 | 0560 | 0561 |
| 2" | 0519Q | 0564 | 0565 | 0566 |
Gauging external taper
threads using a taper ring gauge |
Gauging internal
taper threads using a taper plug gauge |
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These diagrams show the principle of min/max/basic gauging of tapered pipe threads.
The individual specifications should be consulted for full information
