Originally Posted by
BCRider
The hole in the crown can be used for caliper brakes if they reach the brake track on the rim for a 700c wheel but generally on canti boss forks that hole is actually intended for mounting a fender.
Bingo. The rigid fork on my older Trek MTB has canti bosses set for it's OEM 26" wheels and also has a hole in the crown but even with 700c wheels the hole to rim dimension would require long or extra-long reach calipers. I used the crown hole to fasten a fender bracket.
I think I'd ask the seller for a refund as the fork is not as promised.