Description
2 x 0.81 BA HSS Tap Set
HSS BA Hand and Machine Tap Set.
British Association - in 1884 the British Association for the Advancement of Science adopted a thread form and series, primarily for use in precision equipment.
It was inspired by one used in the Swiss watch and clock industry, and was formerly sometimes called the Swiss Small Screw Thread System; but is now just referred to as the BA series.
Like the Whitworth thread, it has a rounded root and crest, but the included angle is 47.5º.
Despite the date of origin and the British sponsorship, the BA is a metric series.
Not only is it based on the metre, but the thread frequency is specified in terms of round numbers in the pitch sequence, with threads per metre allowed to fall where it may.
Bottoming Taps have a lead of two threads and are used to ensure minimum thread run-out when tapping to the bottom of a blind hole.
Intermediate Taps have a lead of four threads and are used in most general purpose applications to cut a thread true to a pre-drilled pilot hole.
Taper Taps have a lead of eight threads and are used as a starting tap in difficult or high precision holes.
Manufactured from HSS this general purpose tap is designed for use in medium tensile materials and is for hand or general machine use.
