But Pontypridd coach Lynn Howells, and Caerphilly coach Mark Ring are keeping each other guessing as to the exact line-ups, naming squads of 23 and 24 players respectively.
Howells has included veteran Neil Jenkins in his squad but the world-record-holding goal-kicker is almost certain to watch the game from the bench as his broken thumb is still troublesome.
Ring has lost lock Nic Rouse and backrower Joe El-Abd to England Students duty, and another lock Paul Jones to injury. And Ring has included the oldest player in the Welsh Premiership. Prop Rob Bilton turns 44 next month, he was playing senior rugby before fellow Caerphilly prop Geraint Lidden could walk.
Pontypridd will not want to lose their proud record over the Castletown Men. The two sides have met 10 times in the Welsh Premiership, with Caerphilly still looking for an elusive victory, and with a number of Ponty players packing down against England, perhaps this will be Caerphilly's night.
The two teams prop up the Premiership table, with Pontypridd recording two wins from their four games and Caerphilly one from five.
If Pontypridd do as Howells is expecting, they will leap-frog Cardiff and Swansea in the table.
Pontypridd (from): B Davey, E Lewis, G Wyatt, R Johnson, A McLaughlin, S James, J Bryant, J Lewis, N Jenkins, P John, G Baber, J Tilly, M Davies, S Cronk, M Rees, N Hennessy, B Cockbain, D McIntosh, R Parks, N Kelly, K Jones, G Lewis, W O'Connor.
Caerphilly (from): S Tuipolutu, O Ashman, R Howells, G Lewis, H Taufahema, R Boobyer, S Cox, J Thomas, L Richards, A Chilten, L Manning, G Lidden, R Bilton, C Ferris, F Vunipola, R Scuse, D Sweet, M Workman, N Watkins, D Davies, S Grainger, G Jones, A Williams, G Williams.