While dressing I noticed a neat little detail I hadn't seen before even though I've worn the suit in the past: the belt loops.
click images to enlarge
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While it looks like a normal belt loop from the outside, there is actually a smaller loop beneath. This small loop is for narrow belts like the one I'm wearing in the photo.
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All of the belt loops on this suit have an extra one underneath. The suit is from the late '40s/early '50s and was off-the-rack.
These belt loops are just a sign of quality that we don't see on too many modern suits, especially off-the-rack.