Simpson Strong-Tie’s PGT series pipe grip tie brackets are designed for attaching wood rails to metal fence posts. The brackets are available in sizes to fit both 1 1/2-in. and 2-in. dia. pipe, and with both standard galvanized and ZMAX coatings. The PGT2OZ (shown here) is designed for 2-in. pipe and attaches to rails with either 1/4-in. lag bolts or SST’s 1/4-in. x 1 1/2-in. SDS heavy-duty connector screws. Brackets for inside corners and 2-piece brackets are also available. strongtie.com.
Metal Fence Post Brackets
Simpson Strong-Tie's compact metal brackets make it easy to fasten wood fence rails to metal posts

SST PGT2OZ