Scotland center Mark Bennett, Wales center Cory Allen and England scrumhalf Joe Simpson are among the 15-a-side players looking to secure a place in Britain's sevens squad for the Olympic Games in Rio de Janeiro.
Britain announced on Thursday a 25-man training squad for the Olympics. It will be reduced to a final 12-man squad on July 19.
There were six 15-a-side specialists selected. Bennett and Allen are test players who have previously featured in sevens internationals for their countries. Britain said Simpson's inclusion "reflects his ability to cover a number of positions."
Britain coach Simon Amor said "for the 15s players aiming to make that transition, recent sevens experience at the top level was important," while others were targeted "to complement the qualities of the specialists we already have."