Never had a problem like that. I'm guessing you were hammering in the bolts before putting on the nut, this will make them hard if not impossible to fit on. When installing wedge anchors put the washer & nut on first then hammer them in. Make sure the nut is up on the threads a way not right on the edge.

Always by full unopened boxes not the loose ones, this is how you get nuts that are the wrong size.

Make sure you drill deep enough with your hammerdrill, make a mark on the bit if you're having problems gauging the depth. Don't sweat it if some don't make it all the way in, just put in another one. If you can't handle seeing too much sticking out cut off the excess instead of trying to back it out.

Al

Al, I don't think that he is using wedge anchors. It sounds like he is using machine bolts. But you can still be on the right track. If the holes were too tight, you can screw up the threads hammering the bolts in.

Usually you want to make the holes 1/16" larger then the bolt size and if they don't fit easily, use a impact driver and screw them in.

The problem can even just be saw dust filling the threads.

Mark

What skregg said. Thinks its bad with 1/2"? Try 3/4" and 1" diameters. The solution for me was a big ol' tap and die set. And a big ol' breaker bar and a pipe section. After cleaning the threads, I sprayed a cold galvanized coating on them and ran the nuts on the all-thread rod while wet. Because the ends were exposed, they later got a double spray of black Rustoleum. Works, but I still need to maintain the exterior ones every few years.

My current project...a pergola...required 20 1/2"x6" galvanized carriage bolts/nuts. I bought them at Lowes, and they all threaded without any problems.
Maybe you got a bad batch, or you damaged the threads...or some debris was caught on the threads, from whatever you drilled thru.

when I buy large bolts/nuts, I thread the nuts on at the store (with the washer), so that they don't get lost, and are just where I want them. This also guarantees a good fit, and also that I have an equal amount of all 3. I do buy a couple of extra nuts/washers, just in case...cheap insurance.

steve

I'm with Steve. If I pick them up in loose quantities, I always put the nuts on. I usually buy in box quantities and it is rare that they don't work together.

In my case, I bought galvanised redhead trubolts, their nuts ran fine but I needed more nuts. ½-13. they won't even start. Their nuts run fine on the same bolts, store-bought nuts don't. Tried wire brushing and thread cleaner with no effect.

But later I drove 60 miles to a big hardware store and bought galvanized nuts which work fine. Oh well.

@harry wookiee Galvanised bolts are oversized compared to regular bolts because of the coating thickness, and won't reliably accept regular nuts.

Galvanized nuts are machined with an oversized hole to accept the difference. It's done this way because otherwise they'd have to thin the bolt out too much, weakening it.

Tldr: galvanised nuts only when using galvanised bolts

Ang Davies hopefully they figured this all out on the 16 years since the original post................