I'd like to change me trailer hitch coupler.

[Merlin]

@charliem is the side bolt guru. We'll see if he remembers 

[charliem]

From my original posts: "I considered stainless bolts, but went with ½" dia. 13 TPI Grade 8 high strength bolts so I could torque them to 80 ft-lbs. Six ½" x 0.1' thick washers were added to each side to make a tight stack when torqued. The side bolts were drilled 2.25" up from the bottom of the frame and 1" in from the front edge of the frame. I used 2" long bolts with flat and lock washers." Stainless is tempting but they are not as strong as HS steel bolts.
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[DavidM]

It is sort of a compromise between availability, corrosion resistance and strength as to which bolts you use. I recently went looking for 1/2" Grade 8 bolts for a similar project, the ones Charlie used, and couldn't find them at an auto parts or a hardware store. So I used Grade 5 which is about 120,000 psi tensile strength vs 150,000 for Grade 8.

I think either would be fine for this application.

David

[Merlin]

I assume Charlie's frame is a 2X4 and the 13 is probably a 2X3. That likely means the hole will be less than 2.25" from the bottom on the frame on the 13. Be sure to look inside the frame under the coupler to make sure clearances are ok for the chosen hole location. I drilled hole for my bolts (2X3 frame) in the center of the frame about an inch from the end.

[Sylvain]

Thanks a lot guys!  Once again lots of great information here.  I noticed on Charlie's photos that he had to add a few washers between the coupler and the frame to fill the space.  I may not have to do that since our coupler seems to sit perfectly againts the frame.

[charliem]

Fewer washers are better. Just be sure any gap is filled. As for grade 8 vs grade 5 I think you would be ok with the fives on a 13. I really didn't run calcs to decide on the grade 8s. My engineering brain just said more is better and the hitch had been a high stress problem for me in more ways than one. Grade 5 bolts will require a lower torque value.

[Sylvain]

Ok, thanks again for the valuable information Charlie.

[ADR]

It is sort of a compromise between availability, corrosion resistance and strength as to which bolts you use. I recently went looking for 1/2" Grade 8 bolts for a similar project, the ones Charlie used, and couldn't find them at an auto parts or a hardware store. So I used Grade 5 which is about 120,000 psi tensile strength vs 150,000 for Grade 8.

I think either would be fine for this application.

David

Do you have the Tractor Supply stores- they have them- sold by the pound.    Grade 5 and 2 also.

[Sylvain]

Tractor supply store. Ok, that's another option.