FWIW - Here is my petcock extension & parts I used for my CSF 2888 radiator:
1. Fragola 460410-BL 4AN to 10MM x 1.5 adapter
2. (2) Fragola Pro-Flow AN Hose End -4AN
3. Fragola 480604-BL 4AN Flare Plug
4. Fragola Black Braided Pro-Flow AN Hose -4AN
Here is a good thread about this very subject:
https://forum.ih8mud.com/threads/csf-2888-radiator-drain-petcock-threads.1053073/#post-11611344
See post #13 & #14
Here is a 50MM extension: Pipe Fitting 1/8" NPT Female to Metric M10 M10X1.5 Male Brass Adapter N-#AC | eBay - https://www.ebay.com/itm/162531629821
Here is a 100MM extension: Fitting for Tooling Pipe to Metric 1/8" NPT to M10X1.5 Male 100mm Long | eBay -...
FWIW - last year I installed a new CSF 2888 radiator that had a plastic drain plug. I removed the plug and installed a homemade extended drain line. The plastic plug that CSF uses is a M10x1.5 unit.