https://www.amazon.com/dp/B097N32G38/
The smooth version is what you need except if you have a very old version of the SWX1.
The second time around, I bought these, which are too long. I then measured it to a bit over 14mm, cut it with a hacksaw, then used tools to sand it to 14mm, and a fine, round file to slightly round the edges by hand. This gives .5mm more length (so it fully contacts the aluminum heatsink) and eliminates the tubing from it entirely.
https://www.amazon.com/dp/B097N32G38/?th=1
Heatblock portion is M6 x 5.5mm. Smooth portion is m7x14mm (although most are actually 13.5mm)
total length 20.5mm
Only the very old X1s use threaded heatsink bores. Newer is all smooth.
They all seem to be the same (all list 13.5mm smooth portion, even though the stock one is 14mm).
https://smile.amazon.com/dp/B097N32G38/
I bought this and am planning on cutting it down by 4mm This leaves a 1mm gap for the bowden tube, and will increase my Z offset by 2mm (I can live with a build height of 398). I could cut it down by 6mm (14mm like original) but then the bowden tube would not sit recessed. I'm not sure how much that matters. If you had a drill press, you could always drill out a new bowden insert.
I'm trying to minimize how much bowden tube I have inside my hotend.
https://smile.amazon.com/dp/B0B53MDDVK
It comes with 5x so I don't mind experimenting.
If you want to save money, you can get them for like $3 off aliexpress, but it'll be slow to arrive.