Can anyone tell me what cooling head I can use to replace the one that broke off my Trinity Extech .24 (yep it finally happened !)?

Thanks!

Sirio or Werks heads will fit not problem.. Other may also, but these will for sure..

Do I need to use a head from a .24 engine or can I use one from a .21 engine?

just match the bolt pattern...try the head from your Werks b5....should fit...if it doesn't, it'll be obvious.

From a .21 is fine.. The Head bolt pattern is the same on all the Sirio based engines.. An Orion head will work too, .21 or .24..