Because I eliminated my in-cab tank, I wasn't sure how I was going to fill the open hole in the cab. In the past, I would have made a filler panel and welded it in, but because I was trying to keep the original patina, that wasn't an option. I was going through some stuff the other day and came across an old mag wheel cap that measured out perfectly. I needed a way to secure the cap, so I went to Lowes and got the stuff I needed. I bought a 4" expanding pipe plug ($4.99) and a bronze bushing with a 1/4" i.d. and a 3/8" o.d. ($2.91).
To make the cap fit flush to the cab's filler neck grommet, I milled down the four raised areas inside the cap and opened the 10/32" hole to 1/4-20. The cap is soft, so I just ran the 1/4" tap down the existing hole and used a lot of penetrating oil to lube the tap and flush out the chips. I used a section of the pipe plug as the backing plate, as because it has a bevel on the backside, it'll fit perfectly into the cab grommet.
I popped the bronze bushing in the center hole and did a test fit using a 1" 1/4-20 bolt and washer.
Here it is in it's installed position. It's nice and tight, also waterproof!
