How do you know a front end will fit your (different) bike ?

[Patrick]

I sometimes see pictures of bikes that have a completely different front end to the rest of the bike - even eg a modern Japanese set of forks on an old British bike ? How do you know if your forks and frame are interchangeable, or is there always some fabrication that must be done ?

Thanks

 

[guardrailjim]

It the fork tubes are the same diameter, they should fit with no problem.

 

[bassguitarist90]

forktube diameter if just doing tubes, but if doing a whole front you must pay attention to the fork stem size and diameter