If you have 3/4 pin seat posts, get 2 PVC T's and about 4 ft of pipe to fit. Put a 4-5 in piece of pipe between the 2 T's and square them up. With them pointing behind seat measure from recess of top T to outside edge of seat back. Then cut 2 pieces of pipe 2 inches longer, insert them into the T's then on the bottom piece install a 90 degree elbow pointing up and on the top one another T. Measure and cut a piece of pipe to fit between them. Then put another piece about 12 in into the top T. Fit all this together and install umbrella and check everything out before gluing together. This is for a Sunbrella. If using another style then you will need to use reducers up or down to fit on the out side T and Elbow. This should get you started.