Factory seatbelt bolts for 1979?

[Tonka]

Does anyone know what kind of bolts I need to buy for my '79 cabs factory seatbelt mounts? My new seatbelt set came with the completely wrong hardware set. The bolts it came with included corresponding nuts.  Why, I don't know, as the truck's factory seatbelts bolted straight up to the cab. The 3 point set was supposed to include directions as to how to mount them and it was more like a warning on not to mount two seat belts to one mount. I called them up explained the situation to their completely unknowledgeable c.s. rep. and it was like talking to a wall. After numerous times being bounced around, the vendor sent me out a different set of bolts. Bolts arrived later that week and they were huge and not even close to right size. 

 The first set they sent me included two huge flat washers, some plain washers and some lock washers. What goes where? Which way do I mount the "L" bracket on the floor?  No info on torque specs included either!

When I called their customer service back to explain they told me to get them from a junkyard... Not exactly confidence inspiring to pull rusty bolts out of a dilapidated cab and not only that, I paid for the correct hardware so I should get it! I paid good money and I think I should receive what they advertise!   
 
At any rate I'd love to solve this dilemma.
 
Any help you can provide is greatly appreciated! Thank you!

[76LongBox]

Not sure if they are the same or not, but the seat belt bolts in my '76 GMC are 1/2" bolts with a 13/16" head on them.

[Tonka]

Thank you very much Long Box. I will buy one of those and see whats what. Thank you again for your help

[Tonka]

So I took the truck to what I consider to be the ultimate bolt bin mecca hardware store in my area. Me and one of the guys went back and forth through every bolt they had till we figured it all out. All three bolts were completely different. The one on the bottom closest to the door we could not figure out. Closest we came was a sloppy loose 7/16. I'm gonna wind up putting a bunch of teflon tape and loctite on it and see if that helps. The ones on the top mounted to the cab were weird also requiring a lot of back and forth and eventually we found what we needed.  The ones in the middle that hold the female end of the belt were the only ones that didn't have us stumped and was pretty straightforward albeit they were fine thread.
Chevy, chevy, chevy... Why do you do the things you do!

Now on to the install! Thanks again Vile! At least the half inch was a good starting point!!

[roundhouse]

The ones that are sloppy.   If you can access them underneath.  Get some longer bolts and put nuts under the floor

[bake74]

So I took the truck to what I consider to be the ultimate bolt bin mecca hardware store in my area. Me and one of the guys went back and forth through every bolt they had till we figured it all out. All three bolts were completely different. The one on the bottom closest to the door we could not figure out. Closest we came was a sloppy loose 7/16. I'm gonna wind up putting a bunch of teflon tape and loctite on it and see if that helps. The ones on the top mounted to the cab were weird also requiring a lot of back and forth and eventually we found what we needed.  The ones in the middle that hold the female end of the belt were the only ones that didn't have us stumped and was pretty straightforward albeit they were fine thread.
Chevy, chevy, chevy... Why do you do the things you do!

Now on to the install! Thanks again Vile! At least the half inch was a good starting point!!

      So after all that work you did not write down the sizes so you could share.

[Tonka]

     So after all that work you did not write down the sizes so you could share.

I'm under the impression that Chevy (GM) just throws what ever they feel like putting in whenever they do the seat belts. The company i ordered the set from sent me two sets and neither worked. The same held true for the size recommended to me by a previous poster on this thread. All I know is all 3 bolts were different and one was barely correct and fit loose. I wrapped that sucker up with teflon tape and it held but it is not the correct bolt.

Also upon further investigation the seatbelt set I received only included one 90 degree L bracket and both the retractor and female end require them. I'm currently fabricating a set out of hardened steel angle iron for the female ends. Trying to do a nice job on them (shaping them, rounding off all sharp edges and priming/painting them red). They're coming out nice but drilling and cutting on hardened steel aint easy and nor was this cheap. I have over 50 dollars in material and drill bits.

The cheap set of seat belts was not the right option.