i thought 50mm was the spacing on gibbo bridge humbuckers.
It varies - Burstbuckers and 57 Classics are 50mm (maybe even 49, I'm not sure) for both neck & bridge, but the more "modern" bridge models like 490T, 498T, 500T and Dirty Fingers are wider, about 52mm.
I think they may even have come up with the concept before Duncan's Trembuckers or DiMarzio's F-Spacing, but they don't make such a song and dance about it.