Key Concepts
L1 Gauge: This is the primary gauge. It checks the functional size (pitch diameter) at the hand-tight engagement point. It's a tapered plug (for internal threads) or ring (for external threads) with a notch or reference plane.
How to Use for External Threads (e.g., Pipe Ends)
Start with the L1 Ring Gauge:Screw the L1 ring gauge onto the pipe thread by hand until it's snug (hand-tight).
Check the position: The end of the pipe should align with the gauge's reference plane (notch) within ±1 turn (plus or minus). If it's flush or within this range, the basic pitch diameter is good.
If it's more than 1 turn out or in, the thread fails.