Connect 1/4" BSP tapered (R1/4 / BSPT) to 1/16" BSP tapered (R1/16 / BSPT)

Stepping a R1/4 port down to a R1/16 fitting uses a tapered BSP (BSPT, BS 21 / ISO 7) reducing bush: a male R1/4 on the outside and a female R1/16 inside, both to the same tapered BSP form so they seal on the thread flanks with PTFE tape or paste. The major diameter goes from 13.157 mm at R1/4 to 7.723 mm at R1/16. This is a single stocked reducing part; the step is two nominal sizes.

Both ends are the same tapered BSP standard, so the only thing that changes is the size; do not swap standards at the same time. If you need to cross to a different thread form as well, add the correct thread adapter rather than forcing a same-standard reducer to do two jobs.