the widely-used pipe thread are NPT & BSPT, both pitch are specified in terms of TPI

the widely-used fastener thread are ISO metric screw threads (M) & Unified Thread Standard (UTS)

ISO metric screw threads (M) has coarse & fine type

Unified Thread Standard (UTS) has coarse (UNC), fine (UNF) and extra fine (UNEF), the pitch is specified in terms of TPI

the widely-used fits is
1) ANSI B4.1-1967 (R1999) - inch
2) ANSI B4.2-1978 (R1999) - mm
3) ANSI B4.4M-1981 (R1987) - mm
4) BS 4500:1969 - mm

the most common standards for Taper-pin & Reamer is
1:48 (ANSI)
1:50 (ISO)
surprisedly, the angle of Reamer is specified as twice the angle of Taper-pin


1) purpose of "preheat" to slow down cooling rate of the weld

2) purpose of PWHT
* post heating ( to reduce hydrogen induced cracking @ HIC )
* stress relieving ( to distribute residual stress evenly )


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