They are shipped with 1/16" nylon washers/spacers to add between the loop and the kydex shell. As pictured has a built in 1/8" thick channel, plus one 1/16" thin rubber washer which fits on my wilderness 5 stitch belt tight enough to hardly move forward or rearward. All you need to do is remove the screws, add the nylon spacers to your desired thickness, re attach the loop with the screws and you're set!
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While I would prefer exact fit on my 1 1/4 inch belt, 1 1/2 is not a deal breaker and would still work well as long as the loop is sufficiently rigid to prevent flexing outward. Exact fit to a belt width is more critical with holsters than with magazine or light pouches.
+1 On the Kytex mag holder. Ready tactical also makes a similar low pro design. Both are rock solid in all temp extremes. Been using both for well over a decade, beat the snot out of them from daily carry to long days out in the woods and they keep coming back for more. These are the original two i bought so as far as holding up to abuse, yeah, they can take it. SKD has the Ready Tactial pouches.,