In the National Bowl last eight, reigning champions Burry Port have to visit Amman United, the only team to beat them this season.
The 2016 runners-up, Taffs Well, head to Caerphilly, while Cardigan host Milford Haven in an all-Pembrokeshire battle.
A large crowd is expected at Constructaquote Stadium where Taffs Well are aiming to go one better than last season when stumbling at the final hurdle.
The Castlemen defeated Wattstown in the fifth round and are seeking a return to their glory days when they reached two major finals, the Parker Pen Shield Final in 2003 – and the Swalec Cup final against Neath in 2004, losing both ties at the final hurdle.
WRU National Plate
Nant Conwy v St Peters
Pwllheli v Abercarn
Penallta v Nelson
Ystalyfera v Rumney
WRU National Bowl
Amman United v Burry Port
Caerphilly v Taffs Well
Cardigan v Milford Haven
Swansea Uplands v Cilfynydd
