Fish plates are the square plates which the U bolts go thru and hold everything together, always pays to have a set of U bolts,nuts and a fish plate in the spares box, usually find mild steel washers are used and these distort/collapse, bolts won't hold tension and U bolts then get loose and things break, using HT washers means things should stay tensioned and safe. When I checked mine after I bought it I found crushed/distorted mild steel washers .