I got the bolts out of the harmonic balancer on my 72 318 Dart,.. So now I had to find a puller that would work, the one from advance auto did not seem like it would work, so I went to harbor freight & got a harmonic balancer puller, but the bolts that come with it did not fit, So I had some bolts that seem like they was going to work, but may not, one gos in by hand, but other 2 do not!.. So what size of bolts do I need for the puller for a 318 harmonic balancer???

5/16 x 18 tpi x 3/4 long is what the AMK site shows.

https://www.amkproducts.com/bulk-fasteners-products/?Product_ID=11605

If they thread in without the tool in place it could be the slots in the tool are not 100% on center exactly. If that is the case the slots in the tool need opened up a small amount.

Have you checked/cleaned the threads on the damper beforehand?

5/16 -18 is the thread size. Do be careful with our import buddies as they sometimes screw up (no pun intended). Any local home improvement store will have what you need.
FYI 5/16 is the outer thread diameter, and the 18 refers to 18 threads per inch.

if the original bolts thread in easily you likely have been bit by "you want cheep, maybe wuhk, or gualantee to wuhk"

I'm no good with bolt sizes, the first one I did I took one of the bolts that came out to the store to match up with longer ones and they've been in the bag with my puller ever since.

Be very careful with the center screw. I can not tell on that one but I have seen some cheap tools that do not have the correct center bolt tip/spacer. When you tighten the screw it gets into the threads on the end of crank and messes them up.

Just a thought.

I have a pretty nice removal/install tool . The other day pulling a balancer the center pin did wedge into the threads slightly. But it was my mistake. Shouldve been turning the nut. Not the inner shaft.

that is why you leave the bolt less the washer in the crank.

or a grade 8 washer on the end of the puller that is larger than the crank bolt hole.
a simple dab of rtv will hold the washer in place, and makes the washer easy to remove when done as well.

Well, I seen my mistake right after I got on hear last time, I had the round part backwards, my bolts was not flat, turned it around they went in & I got it to work & got it pulled off!

great to hear.