I built much smaller frames with extruded aluminum.
It may have been a sliding door track, possibly for a shower door?
It had a square 'U' with a tail. The panels fit very loose in the U.
Squirted silicone in the 'U', put the pieces around the panel, used the 'tail' to connect the sides together and monunt the panels.
Butal rubber caulking may be better.
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