British Standard pipe parallel thread
The British Standard pipe parallel (BSPP) is used primarily for threaded ports and is similar to SAE straight thread. The male has straight threads and an o-ring. The BSPP female has straight threads and a sealing face. The seal is made at the o-ring on the male and the sealing face on the female.

British Standard pipe taper
The British Standard pipe taper (BSPT) male has tapered threads The BSPT female has tapered threads. The seal takes place by deformation of the threads.

Metric Thread
The metric thread is similar to the SAE straight thread as the seal is created by an o-ring on the male creating a seal on the smooth face or surface of the female.

ORF Seal
The ORF seal system consists of a flat, finished surface on the female connector's flange and a recessed o-ring held in a circular groove on the male. The seal is created as the flange and o-ring make contact as the female nut screws onto the male thread. A secondary seal is made as the male connector is drawn into contact with the flange. The back-up seal also prevents extrusion of the o-ring under extreme pressure. ORF provides a better seal in high vibration, high impulse or high torque applications.