Wheel Spacers

Good afternoon all, I’m  looking at Fitting some 5mm wheel spacers as i have just fitted some Bola alloys which are 8.5 wide, i hade the usual 15 and 20 mm spacers on but now these are too wide, although I’m  fitting the 15’s to the rear now as they’ll go nicely, anyhow.. as im looking around I’m noticing that the 5mm spacers are coming with 35mm blots, now.. i thought they should come with 30mm bolts as the standard ones are only 25mm? Or am I missing something?....