Precision CNC collets, various sizes available for multiple spindle types. 
 
*Only imperial ('Merica) tool sizes currently available*
 
ER11
1/4" (0.25")
ER20
1/8" (0.125")
1/4" (0.25")
3/8" (0.375")
1/2" (0.50")
ER25
1/8" (0.125")
1/4" (0.25")
1/2" (0.50")
5/8" (0.625")
ER32
1/8" (0.125")
1/4" (0.25")
3/8" (0.375")
1/2" (0.50")
 
Be sure to check that you select the correct collet that fits your spindle, as well as the desired shank diameter.