Check the listing for details. Wilson rockwell tester spare part aluminum mount ring ,. Condition: New. Listed at 17.56 USD. 21BA13U08 up for sale is a part that came from a closed machine shop , we believe it was from a wilson rockwell tester unit , this aluminum disc we do not know the part numner or where it fits on the unit but it measures 3.257 outer diameter x 0.361 thick and has a center hole that is 1.452 and has some cast features that extend into this space too, the flat side has a machined surface and a small metal bushing pressed in that is 0.416 diameter inside this bushing , and this plate has 4 1/4-20 tapped holes on about a 2 1/2 bolt circle , nice part , we just dont know where it is used on the rockwell tester and do not have the part number , if your a wilson pro or know where this is used or the part number let us know so we can better list it , comes loose as shown in the photos , appears to be a new part , see our store we add new items weekly , thank you for viewing our store and supporting a USA based small hometown business , thank you rwk