There are great advantages in choosing an arch made from plastic-coated tubular steel, and there are many styles available in kit form. In spite of their lightweight framework, such arches are extremely strong, will not need to be painted to prevent rust, and can be delivered to your home. The component parts interlock, providing a wide array of styles that will enable you to create an arch designed to your own specification. If you would like something more substantial, you can commission a blacksmith to make a traditional metal arch or a more modern structure of steel posts or girders. The instructions here are for a classic Gothic-style arch, 4 feet (1.2 m) wide and 8 feet (2.4 m) tall.
Once you have unpacked the kit and checked each item against the instructions to see that all parts are there, separate the eight upright sections and four of the moisture seals. Place a seal over 1 end of 4 of the uprights.
Insert one end of the remaining four uprights firmly into each of the moisture seals from step 1. This will form the four straight sections of the arch: the front and back of both the left and right sides.
Loosely screw the T-joints into position an even distance apart. Join a front upright section to a back section with two of the spacer bars by inserting them into the T-joints.
The spacer bars hold the arch together and prevent it from twisting. You may find it easier to fit the spacer bars by balancing the uprights on the ground.
Fit two spacer bars to each hooped front and back, then join the two sides together at the top with the short spacer bar and a parallel clamp at each end. Secure the clamps with nuts and bolts and tighten with the Allen wrench. Fit the finials between the parallel clamps.
Use a club hammer to place the post at the marked depth. Then, remove the holemaker carefully. The hole-maker should be marked at the correct depth, but if it is not, make your own marking to ensure each hole is exactly the same depth, about 12 inches (30 cm) deep.
Use a level to check that the posts are vertically set. Slide a moisture seal onto the top of each post, then set the top hooped section into these seals to complete the arch.