Stair tread connector (5)
I believe the answer is:
'stair tread connector' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for riser that I've seen before include "found on the staircase" , "Part of flight" , "Vertical piece between treads of staircase" , "Person getting out of bed" , "Upwardly mobile type" .)