In article 1126114314.442240.194730
@z14g2000cwz.googlegroups.com,
says...
Hi group, I am looking for threaded sleeve, with a round OD.
Specifically I require .500 round OD, with 3/8 NC thread ID. I have
looked at MSC, Small Parts INC, and a host of other places, and unless
I have overlooked it, I have struck out. Thanks in advance for any
help you can give, ron

If you have some flexibility on either OD or thread (.500 x
5/16-18, or .625 x 3/8-16), Misumi can help.

http://www.misumiamerica.com/SearchResults.aspx?
ProductValue=u-sfrw

Ned Simmons