Use Product Options Menu to Select Wheel Mandrel: 
Left Side Mandrels (as you face it): A-WM-5 (current lathes- built in 2002 and later with 5/16" motor shafts) or A-WM-3 (lathes older than 2002 with 1/4" motor shafts)

Right Side Mandrels (as you face it): A-WM-6 (current lathes- built in 2002 and later with 5/16" motor shafts) or A-WM-4 (lathes older than 2002 with 1/4" motor shafts)

Current models of BL Lathes refers to models built in 2002 and later. These lathes have 5/16" motor shafts. Older models (including Nos. 1 & 5 High Speed Bench Grinders) have 1/4" motor shafts and were built before 2002. 

Use to hold rubber bonded abrasive wheels, grinding stones, sanding drums, brushes and other accessories with 1/4" center mounting holes up to 3/4" thick.