21mm Dia, ER20 Collet, 3/16" d1, 31.5mm Length

Dimar's Collets are purposefully manufactured from softer metal than the tool holder, this will ensure a tight grip on the cutting tool. 

Be sure to replace your collet, 

• If a tool is broken off while in the collet and it has scored or marked the inside or outside of the collet in any way. 
• If noticeable marking is evident on the cutting tool shank, which is called as "fretting". This happens when two steel parts rub against each other. 
• If small visible copper or dark-colored pits or marks start appearing on the collet this is evidence that the tool is becoming worn out.