Connect 1/4" BSP parallel (G1/4 / BSPP) to 1/8" BSP parallel (G1/8 / BSPP)

Stepping a G1/4 port down to a G1/8 fitting uses a parallel BSP (BSPP, ISO 228) reducing bush: a male G1/4 on the outside and a female G1/8 inside, both to the same parallel BSP form so they seal flat washer or bonded seal on the face. The major diameter goes from 13.157 mm at G1/4 to 9.728 mm at G1/8. This is a single stocked reducing part; the step is one nominal size.

Both ends are the same parallel 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.