Hitch & Coupling Heads. SAS FORT B Fortress Hitch Lock, Fits Bradley Hitch Heads. H K Trailers. Secondary Couplings. The Fort B will fit the Alko AK301 head (the hitch will have this stamped in the side), whilst if you have the AK351 head (generally on the bigger trailers), you will need the Fort A hitch Lock.
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