Team administrator Keith Morgan said, "We have received good reports on Tim and Lee Jarvis saw him play at first hand when he coached him at Mounts Bay. He looks to be a very useful addition to our options behind the scrum and with Roger Davies unwell earlier this week this seemed the ideal opportunity to blood him in a home fixture."
After ringing the changes in recent weeks, the coaching staff have opted for a more settled selection against the Steelmen with only three changes in the starting line-up.
Apart from the inclusion of Mosey the only other change behind the scrum is the return of Nathan Rees in place of Chris Czekaj on the wing. In the pack John Yapp comes in at tight-head prop for Kristian Gay.
Saturday's match has an early afternoon kick-off at 1.30 pm.
Meanwhile Cardiff's away fixture at Aberavon next month has been brought forward to Friday 21 November (kick-off 7.15pm).
Team: Tim Mosey; Ryan Howells, Shaun James, Luke Ford, Nathan Rees; Gareth Davies, Owen Ruttley (captain); Scott Roberts, Kieran Crawford, John Yapp, Matthew Veater, James Down, Damian Welch, Craig Everett, Rhys Shellard.
Replacements: Garry Horrigan, Kristian Gay, Adam Powell, Nick Hampson, Garyn Lucas, Lee Jarvis, Craig Morgan
Referee: Leighton Hodges (Bridgend)