So what sizes can you get?

5mm long ? ...screw 3 together.... 8mm long ? screw 2 together im sure the extra 1mm wont matter.

BTU
http://www.technobots.co.uk/acatalog/Online_Catalogue_Ball_Transfer_Units_392.htmlhttp://www.technobots.co.uk/acatalog...r_Units_392.ht ml