When I've had a moment, I've made a few odds and sods for oil fittings.
I found the brass nuts a bit soft and made some stainless ones.
It turns out we have NOS brass nuts it stock, so Anita mentions after I made them.
I also made a breather stub for 1/4" copper tubing.
Both 5/16" and 1/4" copper tubing are kept here.
When I make an order for some larger brass I will make some push over Ferrels.