a photovoltaic mounting system having a base portion with a plurality of rails . the system includes a spring clip unit having a foot configured to hold a pv module coupling device and arranged to slide on one of the plurality of rails . a first spring clip is moveable on the foot from a first position in which the first spring clip is disengaged with the rail to allow the foot to move freely along the rail , to a second position in which the first spring clip engages the rail to attach the foot to the rail . a second spring clip is held by the foot and is forcibly engaged with the rail when the first spring clip is moved to the second position to help lock the foot .