Strong Steel
Gussets may look like metal mesh, but they are strong steel plates with holes in them and metal spikes on one side. The spikes are driven into the two boards to hold them. The gusset is further secured with nails or screws. In factories which make roof trusses, machines force gussets into the wood under great pressure. Individuals making their own trusses can buy metal gussets and drive them in place with a hammer.
Overlap Strength
Metal gussets make a much stronger connection between two boards because they overlap the point at which the ends meet or butt together. The alternative method of fastening is to nail the butted boards together, driving nails at an angle in a technique called toenailing. That has the nails overlapping the joints, but with fewer connecting points and less strength than a gusset.
Rectangles
Some metal gussets are simple rectangles, used to fasten two boards that join at ends or meet at slight angles. This style is often used to splice two boards for parts of a truss or other roof element, like a ridge board, where a single board is too short. In trusses, these gussets are used most often to fasten the vertical or angled webs that brace the slanted rafters.
Peaks
Peak gussets secure the tops of rafters where they meet. There are two basic styles, depending on whether or not a ridge board will be used along the truss tops. Both styles have a horizontal bottom which is fastened to both rafters and slants at the top to match the angle of the peak. The ridge board style includes a slotted opening at the top for the ridge, which sits inside the gusset fastened to both rafters.
Variations
Joist hangers, hurricane clips and similar steel fastening components are types of gusset. Joist hangers are brackets fastened to a beam with a slot to hold a joist; both beam and joist are nailed through the hangers. Hurricane clips are brackets which overlap the end of a truss rafter where it meets the wall. They are nailed to the wall cap board and to the truss to tie the two pieces together.