Connect 1" BSP parallel (G1 / BSPP) to 1" NPSH straight hose thread

G1 and 1-11.5NPSH are both called the same nominal size but are different thread forms: G1 is parallel BSP (BSPP) at a 55 degree flank angle and 1-11.5NPSH is straight NPSH hose at a 60 degree flank angle (33.249 mm versus 32.89 mm major diameter). They start a turn or two then jam without sealing, so a machined parallel BSP (BSPP)-to-straight NPSH hose adapter is required, not tape.

The matching 1 inch label is the trap. The 55 degree versus 60 degree flank angle means the flanks never fully mate; add the correct adapter rather than forcing the joint.