Initial purchase did not meet expectations. I filed down the protruding key to fit my 1/2' diameter pully. The 10mm shaft had a flat which accommodated the shaft adapter to slide on the shaft. However when the adapter was forced on to the 10mm shaft, it made the outer 1/2' adapter diameter larger, and it would not allow the pulley to fit. I purchased the following item instead (am-0333 1.152 in. ID 0.442 in. OD 0.5 in. Brass Spacer) which provided the necessary difference in the 10mm shaft to the 1/2' pulley. I am thankful that both parts were available from Andymark, and thankful too for their prompt delivery.

haven't used it yet, but it looks useful

'Had this item fail multiple times on our 2016 robot. Do not use!
Instead use
http://www.andymark.com/product-p/am-2182.htm
or
http://www.andymark.com/product-p/am-2088.htm'

'Sleeve is so tight that it must be hammered on, risking damage to motor/shaft.'

Sleeve needs filing to make fit and we have broken two of them so far.