I received a metal bed frame without the bolts. Directions have sizes used in hardware list. Went to hardware store but they didn’t have M6 bolts with hex head as shown. Guy suggested Phillips head. I can only screw them in so far. Thought maybe that’s why they use Allen wrench in directions for more leverage. Found Allen wrench shaped device with Phillips head but could only get one al the way in using it. The rest are stripping the head. Do I need to find bolts with the hex head instead and use an Allen wrench, or do I need to drill the holes bigger, or is it the material of the screw?

I received a metal bed frame without the bolts. The directions have the sizes used in hardware list.

I went to hardware store but they didn’t have M6 bolts with hex head as shown. The sales associate suggested Phillips head. I can only screw them in so far. I thought maybe that’s why they use Allen wrench in directions for more leverage. I found Allen wrench shaped device with Phillips head but could only get one all the way in using it. The rest are stripping the head. 

Do I need to find bolts with the hex head instead and use an Allen wrench, or do I need to drill the holes bigger, or is it the material of the screw?