Spear shaft size

hi, I've been searching for some information around the ideal tolerance for enclosed tracks. I've purchased a 9/32 UHMW enclosed track from Neptonics and the local spearfishing shop said a 7.1mm shaft would fit fine in it. Will this be OK given it might get some expansion from the laminated teak and squeeze the track? I've also purchase the 3/8 UHMW for a blue water gun I'm planning to make and had the same question on tolerance? Any help is appreciated. Cheers Peter