Wiring harness clip bolt

[Bob Zone]

My new wiring harness is slightly too large for the brass clip holding it to the nearside frame. The bolt that holds the brass clip goes into a nut that is ?welded inside the frame. I need to order a longer bolt. None of my assortment of metric or bsf bolts have the correct thread - they just start but obviously want to cross-thread. I suspect it may be a BA thread. Does anyone have a description of this bolt? Thanks Bob Zone TC 5995