@pete50 thanks for the response. I don't have a clue which make the TRVs are though. Is there any way of knowing that just by looking at the body without the head?
I am trying to find suitable TRV heads for rads in house I bought earlier this year.
Three rads have the attached pipework which appears to have a TRV pin at the top, but no heads on them, wondering if anyone has seen these before and can recommend a suitable head, or alternatively a suitable...