The most commonly reached-for reducer in the range, converting a 1/4 inch NPT female port to a 1/8 inch NPT female outlet. Countless blocks, thermostat housings, fuel rails and pressure regulators carry a 1/4 inch NPT port, while most aftermarket pressure and temperature senders arrive with a 1/8 inch NPT thread, and this bush bridges that gap in one part. It also lets you reuse an existing port rather than drilling and tapping a new one. Being a tapered thread on both ends, it needs a suitable liquid sealant or PTFE tape on the male taper and should be nipped up progressively until leak-free, checking under pressure before you sign the job off.