A 7/8" - 9 BSW thread tap is a type of thread cutting tool used to create internal screw threads. The BSW thread form is characterized by a 55-degree thread angle.
Differences Between British Taps
Thread Form and Angle:
- ⦿ All use a 55-degree thread angle with rounded crests and roots.
Pitch:
- ⦿ BSF: Finer pitch (threads closer together) than BSW.
- ⦿ BSW: Coarser pitch than BSF.
- ⦿ BSPP & BSPT: Pitch defined by the standard, similar to other Whitworth forms but adapted for pipe fittings.
Application:
- ⦿ BSF: Precision applications needing fine threads.
- ⦿ BSW: General-purpose mechanical applications.
- ⦿ BSPP: Pipe fittings requiring a parallel thread and a sealing washer.
- ⦿ BSPT: Pipe fittings creating a pressure-tight joint via tapering threads.
Sealing:
- ⦿ BSPP: Requires a gasket or O-ring for sealing.
- ⦿ BSPT: Seals through tapered threads, often with sealant.
Practical Example
- ⦿ BSF Tap: Used for threading a precision-engineered component requiring fine threads.
- ⦿ BSPP Tap: Used in a hydraulic system where pipe connections need a leak-proof joint with a washer.
- ⦿ BSPT Tap: Used in gas piping where a tapered thread ensures a pressure-tight connection.
- ⦿ BSW Tap: Used for bolting together parts of a machine where a standard thread is sufficient.
Configurations for Thread Taps
Taper Tap
A taper tap, also called a starter tap, has a gradual thread profile. Typically they have a few threads that are tapered and are used to start threads in a hole. They are designed to be used first in a series of tapping operations.
Plug Tap
A plug tap has a slightly shorter chamfer than a taper tap and is used to continue threading after the taper tap has started the threads. It's a versatile choice for many applications. They are extremely popular and are used for through holes and can even be used to start blind holes.
Bottom Tap
A bottom tap, also called a bottoming tap, has a very short chamfer and is used to thread close to the bottom of a blind hole where a through-hole doesn't exist.
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