What does R8-ER20 mean on a tool holder?

Q: What does R8-ER20 mean on a tool holder?

Short answer: `R8-ER20` is a R8 machine-taper holder fitted with an ER20 collet chuck; it holds tools from 1 mm to 13 mm shank diameter. The R8 end goes into the spindle (R8 shank, common on Bridgeport-type milling machines), the ER20 end grips the tool. Collet range is set by DIN 6499. A 12 mm end mill needs ER20 or larger; an ER20 will not close on a shank outside

Question

Accepted Answer

Short answer: `R8-ER20` is a R8 machine-taper holder fitted with an ER20 collet chuck; it holds tools from 1 mm to 13 mm shank diameter. The R8 end goes into the spindle (R8 shank, common on Bridgeport-type milling machines), the ER20 end grips the tool.

Collet range is set by DIN 6499. A 12 mm end mill needs ER20 or larger; an ER20 will not close on a shank outside