NPS 1-1/4 Pipe
Outside diameter 1.660″
OD in mm 42.164 mm
NPT thread 1-1/4″ NPT (11.5 TPI)
Every NPS 1-1/4 pipe has this OD regardless of schedule — the schedule changes only the wall thickness and bore.
Schedules
| Schedule | Wall | Wall mm | Inside diameter | ID mm |
|---|---|---|---|---|
| 40 = STD | 0.140″ | 3.556 | 1.380″ | 35.052 |
| 80 = XS | 0.191″ | 4.851 | 1.278″ | 32.461 |
1-1/4″ NPT thread
| Designation | 1-1/4″ NPT |
|---|---|
| Threads per inch | 11.5 |
| Recommended tap drill | 1-1/2″ (1.5000″ / 38.1 mm) |
NPT is a tapered thread (3/4″ per foot on diameter) — it seals on the thread flanks with sealant. The size refers to the pipe's nominal size, not any measured thread diameter.