The original 'pip pin', manufactured by Avdel in England and now no longer in production.

The registered trade mark pip-pin® has become a general term for a ball lock fastener.

The 3201 series pip pin was a steel double action pin with it's characteristic loop handle.

The pip pin was sized by diameter in 1/16" and grip in 1/10" , so a 0615 was 6/16" diameter with a grip of 15/10", and this number was stamped on the pin - 3201-0615

The pip pin was originally supplied cadmium plated and was approved by AGS as AGS 2105-xxxx

SDM 205, CAA E1130

Above - stamped 3201 sizing