I have a workmate 550 ?

They are probably roll pins, available from any good hardware shop. Not that there are many nowadays!

Ron
July 2009

Looks like part #30

http://www.toolsandpartsdirect.co.uk/store/parts.asp?MODEL=WM550-----A&PARENT=172&HEAD=¦1¦Black%20n%20Decker¦6¦Indoor¦42¦Workbench,Vice,%20Jobbers,%20Ladders¦172¦Workmates

Dave
May 2009

Not sure but it sounds like roll pins which you need. Either look under "Engineering Supplies" in the yellow pages or go to a tool or hardware shop - they sell these in assortment boxes but sometimes they have a box open from which they sell items singly.
A split pin might do either but the ends would be sticking out and could be a hazard.

JD
April 2009