No one (in the hobby business) is going to get rich selling screws or even pay the power bill, but you have to wonder why the LHS operator just doesn't buy the common size screws in bulk and repackage them himself. Offer two or three times as many as are in the Walthers packet for the same price, or he could even sell screws individually. The dime screw that gets the customer in the store might lead to a thirty dollar impulse purchase.
The profit margin for fasteners is small but helps sales of other items by providing tools/parts to repair them if they break or upgrade them.This encourages the customer to come back and buy more of the same or other items.
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