Do rivet nuts work?

I have used them for over 40 years and they do have certain drawbacks , I try and use the riv nuts with the knurled out side perimeter, the knurled type have a considerably better grip, My preference is to use the weld on nuts whenever possible .
 
The seat belt topic has been discussed on this site before and would be worth looking up, before starting. Mounting belts to the body and how the body is secured to the frame among other issues come into play.
Seat belts may give a false sense of security if the integrity of related parts aren't considered in the process.
I don't mean to be negative, just want you to have a more detailed picture before you start.
 
Superhart said:
I appreciate all your responses. I have read everyone of them and thought carefully about everything you guys have said. I have finally decided how to handle this situation. I will remove the two seats, install two lengths of steel bar, length wise under the floor of the car. The two bars will be 36 x 2 x 3/8. I will attach them to the underside of the cabin floor with steel pop rivets. Then I will locate, Mark, drill and tap these bars for 3/8 inch diameter bolts And tap threads into the bars. Then I will use 3/8 inch bolts to secure the two seats to the floor of the car. I feel as though this type of installation will be quite strong and strengthen the steel floor as well as provide a very secure
Mounting for the seatbelts. How does that sound to all of you? Comments, anyone?
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Sounds like a plan. If it were me I would probably also add a washer and nut to the bottom of the bolt, after it has been threaded through the plate, but that is just me.
 
Again, thanks for great suggestions. Maybe it would be better to use screws to attach the steel bar to the car body rather than rivets. It’s more work, but perhaps better in the long run. Instead of the cage nuts, I will drill and tap the steel bars to act as nuts for the bolts attaching the seats to the car. I do need to be careful, though, and work within the confines of the tools and equipment that I have available. I have no access to a welder, overhead lift, vice, etc.. All I have are basic hand tools, a tap and die set, a power drill, and a rivet tool. Literally, therefore, I am by definition a shade tree mechanic.
 
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If you're going to solve the problem by threading the bolts into the bars, you are going to need some way to prevent the joint from loosening under vibration. I suggest a locknut. A nyloc nut might work, or you could go for the period look by using a castle nut and cotter pin. You would need to use drilled bolts but I bet there's a drilled bolt in the standard Model A fastener set that would suit this application.
 
5/18x18 would be fine - it's what Detroit uses. Making the mounting strong enough that it doesn't tear through the floor in a crash is the goal. A 2-3" 1/8" flat plate tacked to the floor should be enough. That will also be thick enough to hold the RivNut. My seat mount is 1x2 .090 tubing with RivNuts.
 
I was always taught that the thickness of the nut should match the diameter of the bolt. I am using 3/8 inch bolts to mount the seats so I will use 3/8 thick steel strips and tap them 3/8 to match.
 
Superhart said:
I was always taught that the thickness of the nut should match the diameter of the bolt. I am using 3/8 inch bolts to mount the seats so I will use 3/8 thick steel strips and tap them 3/8 to match.
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1.5 x dia will get you the max holding power a bolt/nut can offer. % of Thread engagement (class of fit) is also a factor. Fine thread has more holding power than coarse.
 
I've used multiple different type of rivet nuts & nutserts over the years. They are common in aviation. Rivnuts can be sourced with an anti-rotational key formed into the flange. A key slot has to be filed into the hole drilled to accept the keyed rivnut. They are available in open and closed end and in multiple materials from aluminum to stainless steel. Lots of different lengths and thread sizes are available.

If the screw thread protrudes into a swampy area then the fastener can corrode and make it very difficult to remove. A lot of them come loose and rotate in the hole due to this. The closed end type will prevent corrosion of this type if anti-seize is utilized.

A person might consider a model A type D-nut but they aren't much easier to install and near impossible on blind installations.
 
Rivet nuts are threaded inserts into a hole that are crimped into place with a special tool that threads into the rivet then is squeezed to tighten the rivet part of the rivet nut to hold it into the hole. If the hole is not drilled properly or is oversized, you will have problems. If the rivet is not crimped properly you will have problems. If you are in a high torque requirement setting, you will have problems. But if you are doing light duty applications they are great. On 1960’s Mustangs, Ford used a large scale rivet nut for steering arm and clutch pivot frame mount applications. I won’t say they are perfect, but they were pretty effective. I liked the comment I saw above about some JB weld used in combo if you are concerned. If I ever had one that didn’t set to my satisfaction—real simple drill it out and do it over or go to real nut/washer application. I like rivnuts, just choose the application appropriately.
 
After all this discussion about Rivet, and how sometimes they rotate in their mouth, I finally thought of a solution. I may not be the first one to think of this, but I haven’t seen anything in print about this method. I decided to a “keyway“ in the lip of the rivet I wanted to immobilize. Here’s how I did it:
I took a sharp punch and carefully made a dimple in the flange of the rivet. I wanted to immobilize. I then cut length of paperclip to use as my “key“. I took an appropriate sized drillbit that would provide a snug fit for the paperclip. Taking a centerpunch, I put a dimple in the flange of the rivet so that my drill bit would not wander. I then carefully drilled through the flange of the rivet and the metal underneath I then coded the rivet with some clear five minute epoxy And worked the paperclip in and out of the drill hole a few times before leaving it in place while the epoxy set up. I let it sit overnight and the next morning I use a flush nipper to cut the paper clip off flush with the lip of the rivet. On a couple of rivet knots that were larger such as 3/8 inch I did two paperclip keys to ensure that I can tighten the screw to appropriate tightness. It’s only been a few days since I did this but so far everything seems to be working just fine.
 
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