How can I securely fasten a carriage bolt?

Question

I recently made a bracket for mounting a TV onto a custom pipe mount that I built.

I was advised at my local hardware store to use a carriage bolt here for the following reasons:

1. These counter-sunk holes will be flush against the back of the monitor, so there'll be no way for me to make sure that the bolt doesn't twist when I tighten the nut on it.
2. By hammering in a carriage bolt, it will "grab" the edges of the hole and prevent it from twisting.

For anyone who, like me, previously did not know what a carriage bolt is:

(The square block at the top, when hammered into the material you're using, will grab and secure the bolt, supposedly.)

Unfortunately, this setup isn't working the best for me. I have lock-nuts, which are extremely difficult to get onto the bolts. When I try doing it with my drill, it actually strips the backside here and the bolt spins freely.

My main question is this: is there a type of carriage bolt that has some kind of phillip's, flathead, or allen wrench socket on the back to initially setup the tension? My plan for now is to do something with two nuts like this:

1.   2.  3.  4.
|-######-l|--|

1. The carriage bolt.
2. My MDF.
3. A lock-nut and washer.
4. The bracket, washer, and lock-nut. 

I'm thinking that this will secure it really well, but I'll need to provide reverse tension while installing the first lock-nut. Any ideas?

Answer 1

Lock nuts and carriage bolts are a bad combination and even worse when trying to use them in material like particle board or MDF.

You could try to use a Tee nut from the monitor side and then simply use a short hex head bolt into the Tee nut.

Answer 2

Easiest solution is to use a torque washer (pronged washer, no-turn washer) under the head of the carriage bolt. It has a square hole and spikes on the washer.