BSPP BSPT B RITISH S TANDARD P IPE P ARALLEL B RITISH S TANDARD P IPE BSP British Standard Pipe Approx. NPT tap drill chart. List of BSP Series. Parallel pipe size Thread size Threads per inch G 1/8“ 3/8“G 1/4“ 1/2“G Pipe Thread Drilled Hole Sizes. NPTF. Recommended Tapping pipe Drill Size Thread Core Size O/D T.P.I. Imperial Metric Depth Diam//S// See the tables below for BSPP and BSPT pipe sizes and the corresponding threads per inch. BSPT Rp (Internal Parallel) Dimensions Chart. Designation