Just use the 1/4 clevis pin. Your body weight will keep the seat firmly in place. Plus you need the slightly loose fit to be able to get the pins into the mounting holes.

You could use a long 7mm bolt, cut the threaded portion off, and drill a hole in the bolt for a small R clip.

Had some time today and went to get the pins and it seems 1/4 is a little loose,and 5/16 is a little too big.

The holes in the brackets seem to be 7mm (M7x1.0 clevis is impossible to find).

Might drill everything out a hair so the 5/16 fits snug in there...or make a 7mm pin.

HAHAAHAH! Can't fault your logic on that one Dan !

There's your mistake, Mike: you took your wife shopping in the Mini!??

Normally I'd agree with you Dan.  There was one day my wife agreed to buy some type of drying rack and we happened to be in the Mini....when we showed up, it was bigger than had been reported (a good thing I guess) however there was no way to fit it in the Mini.

Although it appeared as though it would fill the entire back seat, we couldn't get it TO the backseat, until a lightbulb came on and moments later, the passengers seat was out, rack was in, and we were on our way.

I think that's the only time I've been "out and about" and needed to pull the seat.  I also removed it one time to install speakers and whatnot, and I knew I'd be climbing in/out 1/2 dozen times so I just yanked it.  Not being as svelte as I was 20yrs ago, it was just easier.

Yes,a lot of people like myself dont have a normal sorted car that is left alone. Like,maybe one day ill take it out to mount a methanol kit for the turbo setup.Maybe in 2 weeks ill pull it back out because i want to put a permanent wideband in.Never ending. Lol

You'd think so, but that hasn't been my experience. A full roll cage w/ rear horizontal bar combined with a spinal fusion make access to the back seat impossible w/o removing the front seats. Today I'm replacing my O2 sensor. The controller is under the dash, so out come the front seats again.

Dan , that is the pin. 

I'm with Onetim on this, though not in his cars!
If you have your car sorted, you shouldn't need to take the seats out very often, and removing two little nuts vs clips or split rings would be no big deal.

Having driven a car with a milk crate for a seat, another with vice grips for a steering wheel, and one with a swing away wheel that wouldn't lock, now with the hindsight of age, a quick release drivers seat would worry me. ??

Is this the type of pin you are thinking of? They are called R-pins (for their shape). Thwy come in all different sizes. Be sure to position them so the tips point downward or in toward the tunnel so they don't catch clothing.

There is a better cotter pin that pulls out and pushes in. No  fiddling or trying to separate the metal to sllde in the hole.

Rosebud

That is exactly what i had in mind. Very nice.Thats exactly what i plan on doing.It seems like a better option all around than the bolt.

I had no idea I'd be removing my front seats as often as I do. These pins make the job a bit easier. 

+1 The exact changes I made to mine, and as I was making the seat brackets I added brass bushings to them.

Mine have just plain bolts, I think they might be 1/4-20, with a steel spring wave washer on both sides of the bracket to keep them from rattling around. I think originally they just had a plain nut, but I upgraded them to nyloc nuts. 

Thanks guys. I was brainstorming thinking a pin would be nicer than a bolt. I was assuming thats how they came from the factory. I am 6'4" and have the brackets to push the seat back some. Like pulling the seat out to make it easier to work on occasionally and also i have a power block,a fuse block,and relays mounted under the driver seat.Ill match up a drill bit to the hole insuppose and try to find some proper size pins.

It's an aftermarket option.  The bolt is correct.  Often, folks (like me), purchased the aftermarket brackets that will give you a little more seat movement and then install the pin/clip to make it easy to pop the seats out if you like.MM seat bracket

I set up my seats with the clevis pins and a spring pin that goes through the hole ( It's a Cotter pin, hairpin, you get them at the hardware store). This set up makes it very easy to remove the seats and replace. They are secure and strong. My mini is my only car and Most days I ride without the passenger seat because it makes living with the mini much easier. When I have a passenger, it takes about ten seconds to put the pass seat back in.