Thermal switch

I am looking for a thermal switch for an electric fan. On at 185, off at 165, with 1/4 NPT. I can't find one from any aftermarket source- they all seem to have 3/8 NPT. An oem switch with these specifications would be great. Anybody know what will work?

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check home depot, i've bought numerous fittings there and adapters

 

Flex-a-lite 31163 - Flex-a-lite Variable Speed Controllers

Summit has this one, 1/4 pipe thread and is adjustable.