NPT Adapters
NPT(National Pipe Thread) Adapter is designed with tapered thread ANSI B1.20.1, to seal pressurized fluid by a sealant or PTFE tape. NPTF(National Pipe Thread Fuel) is dryseal according to SAE J476 and ANSI B1.20.3 standard.
Thread Difference between NPT and NPTF
NPT thread after wrench tight, leave a spiral leak path at crest-root junction, to seal by PTFE tape as figure showed.
NPTF thread assembly, do not leave a spiral leak part, because they have controlled truncation at the crest and root, ensuring metal to metal crest root contact as in figure showed.
NPTF Hand Tight, Crest
NPTF Wrench Tight, Crest to Root Contact
In reality, a sealant/lubricant is necessary to achieve a leak free joint, even with NPTF threads. The sealant/lubricant fills all imperfections in the surfaces affecting the seal and also provides lubrication to ease assembly and minimize galling.
Dimensions of NPT NPTF Adapter Ends
| SIZE | Thread | Drill | Minimum Thread | Thread Engagement |
| PT | D Ref. (inch) | J (inch) | TE (inch) | |
| NPT/NPTF | ||||
| 2 | 1/8-27 | 0.188 | 0.31 | 0.24 |
| 4 | 1/4-18 | 0.281 | 0.44 | 0.34 |
| 6 | 3/8-18 | 0.406 | 0.47 | 0.34 |
| 8 | 1/2-14 | 0.531 | 0.59 | 0.46 |
| 12 | 3/4-14 | 0.719 | 0.63 | 0.46 |
| 16 | 1-11 1/2 | 0.938 | 0.75 | 0.59 |
| 20 | 1 1/4-11 1/2 | 1.25 | 0.78 | 0.59 |
| 24 | 1 1/2-11 1/2 | 1.5 | 0.81 | 0.59 |
| 32 | 2-11 1/2 | 1.938 | 0.81 | 0.59 |
Catalogue of NPT NPTF Adapter
