Gloucester prop Nicky Thomas signs for Scarlets, returning to Wales to "pursue international ambitions".
Wales are set to be without Scarlets loose-head prop Rob Evans for their four autumn internationals.
Scarlets' Wales prop Rhodri Jones boosts his 2016 Six Nations chances by returning after injuries for Llanelli in the Welsh Premiership.
Australia Under-20 prop Cameron Orr joins Gloucester, who also give fellow front row Paddy McAllister a new contract.
Scarlets' new Wales prop Rob Evans signs a contract extension to remain with the west Wales region.