Hi, I'm doing my interior at the moment on my 69 sl and am going to the fastener place tomorrow for metric things and I have one in my kit to take with me to size the correct washers. I tried tapping the holes in the floor and tunnel with a 10x 1.0 whatever that means but the threads are finer on the bolt. Will get the skinny on the the correct size from the fastener place as they have an extensive inventory of metric. I',ll get back to you when I find out the size. I would like some detail on how all the little washers and collars and spring washers fit. I bought this car partially disassembled and it's been two years sorting it out as I don't have any parts manual to go by. Darn near got the new interior installed as it was completely stripped to bare metal including the doors and all the dash upholstery.