2 questions

I bought a set of four Centerline Hellcats in beautiful condition for $350 for 4. The fronts are 15x8 and the backs are 15x10 and they appear to be a universal bolt pattern. I have them on my 88 GMC 1/2 ton right now and I was wondering, what are the other holes for? is it for Dodge and Ford 1/2 ton pickups or is for the smaller GM trucks like S10's? My other question is is what is the widest tire I can put on a 10 inch rim? Someone told me that the widest is up to a 315 but I think that only a 305 will fit half safely. But I do know that a 295/50/15 will fit on a factory 8 inch wheel pretty good so what is the limit on a 10?

Tire width / wheel width depends on aspect ratio. So a 10" wheel can take tires even larger than 325/50.

But you'll want to make sure the tire has enough load capacity. Check the placard on your vehicle for the original tire size, and while your at it, check the GAWR's, too! Choost a tire that has at least the same capacity. If you use the GAWR (Gross Axle Weight Rating) method, divide the GAWR by 2 and multiply it by 1.1, (the 10% is to compensate for a passenger tire being on a light truck), then use that as the minimum load capacity.

Hope this helps.

The tire size also depends on the type of tire. A drag radial with more sidewall flex can pull into a narrower rim size than a standard truck tire etc... As for the other lug holes, you would have to check with Centerline to see what other applications they sell that wheel for. They are the only ones who would know what other vehicles they designed the wheel to fit safely.