Fork crown main tube clamping stud nut, long road holder. 7/16in x 20 x 0.4in H. This is made to original dimensions but it is recommended to use BT-OF-F11M2/643 from the short roadholder with the same thread but reduced hex for easier spanner access. Used 1950 to 1956.Original part number:B2/643; 13459; 16187 - fork crown main tube clamping stud nut- washer not listed in parts book