Connect 2" BSP tapered (R2 / BSPT) to 2" NPSH straight hose thread

R2 and 2-11.5NPSH are both called the same nominal size but are different thread forms: R2 is tapered BSP (BSPT) at a 55 degree flank angle and 2-11.5NPSH is straight NPSH hose at a 60 degree flank angle (59.614 mm versus 59.74 mm major diameter). They start a turn or two then jam without sealing, so a machined tapered BSP (BSPT)-to-straight NPSH hose adapter is required, not tape.

The matching 2 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.