What strain relief for 5f2 chassis?

I can't help you on the "right one", but is your chassis as grainy and rough looking as the one I just got?

 

There is a specific style, which I ordered for my 5f2a. It did take a while researching the right one. If you're in Europe I can probably post you a spare. It's possible there are two different variants, as my initial one sent from Boothill didn't fit my Chinese made chassis (which I think is the most common dimensions for this type).

I THINK You want a Heyco 5N-4. Try looking, there is a PDF somewhere with the dimensions.

Update: checked the dimensions on mine, pretty sure the 5N-4 is correct, the 'flattened' dimensions are just over 11mm, where yours shows 11.8. I do have a spare but they only cost pennies on eBay.

 

Also is that going to be period correct, so it would be more for the two prong cord and you might be wanting to go updated to three prong?

 

My chassis, strain thingy and lead, same dimensions, work fine for three-conductor cable. the cable grip pliers do make it easier, again, they are on eBay etc.

 

What @Paul-T says. IME most amp-specific shops sell the same 'Fender replacement' sized strain relief — though Heyco do make tons of different sizes — that fit in the standard double-D punch-out in most modern chassis types. And that size does fit standard 3-conductor SVT and SJT. I see AES actually has a separate listing for a 2-conductor strain relief. Also as Paul says, save your sanity — if you don’t already have some strain relief pliers...