Connect 1/2" BSP parallel (G1/2 / BSPP) to 1/8" BSP parallel (G1/8 / BSPP)

Stepping a G1/2 port down to a G1/8 fitting uses a parallel BSP (BSPP, ISO 228) reducing bush: a male G1/2 on the outside and a female G1/8 inside, both to the same parallel BSP form so they seal flat washer. The major diameter goes from 20.955 mm at G1/2 to 9.728 mm at G1/8. This is a single stocked reducing part; the step is three nominal sizes.

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.