It looks like a Bosch Rexroth rail to me, but there may be other manufacturers who use the same profile, I don't know.
R160580431,400 MM Bosch Rexroth | Bosch Rexroth R1605 Series, R987261842, Linear Guide Rail 20mm width 400mm length | 409-539 | Welcome to RS Online
Look at the profile on that.
I'm using bosch rexroth size 25 rails on my build. They are quite nice. Those ones look smaller but have the same shape.