59.mm
Single-tapped 5BA with set screw | 59.br1
Single-tapped 5/32W, sharp corners | 59.br2
Rounded, single-tapped, stamped MFEA | 59.br3
Double-tapped, very rounded |
59.br4
Double-tapped, end-stamped Meccano | 59.xx
Mazac, double-tapped | 59.br
Post-war, unstamped, not rounded |