The spacing of a frame/fork is measured from the inside surfaces of the dropouts, where they come into contact with the locknuts of the wheel’s axle. this is called the OLD of the axle.
110mm – Some thru axle front hubs including 20mm and boost standards
142mm rear – thru axle rear hubs
148mm – boost standard thru axle rear hubs
157mm rear – Super Boost standard thru axle rear hubs