Metal stair tread brackets are used instead of wood cleats and for plenty of good reasons. These often become a safety hazard over time, as the wood starts to deteriorate. Metal, will not disintegrate as fast as the wood it is normally attached to. In most custom stair treads cases the wood stringers and steps will suffer from wood rot or termite damage before the metal brackets become a safety problem.
Metal stair brackets, often require lag screws instead of nails or screws to attach the stair step to the stringer. These lag screws are normally an inch and a quarter for the stair treads, if they are built from 2 x materials. For example a 2 x 12 or 2 x 14 stair tread will require lag screws that will not go through the wood step. A 2 inch like screw will easily go through an inch and a half stair tread. If you’re building a stairway, this will be useful information.
Some metal stair connectors have four holes on each side of the metal bracket for the lag screws, while other metal stair brackets have three holes on each side. This normally depends on the thickness of the stair tread and the use of the stairway. Public stairways will normally require the stronger stair tread connector.
During my career of building stairways, I have seen quite a few metal stair tread brackets. Some builders had custom made brackets to meet specific stair tread applications, while others used Simpson products, that are more readily available to home builders and contractors.
One of the biggest problems I have noticed, using metal stair parts is the lag screws can loosen up over time, creating a safety hazard. Warping treads, along with stair steps that split where the lag screw is located, seem to be the biggest problems associated with metal brackets. There are that should be followed when building or remodeling stairways.
Staircases are normally high traffic areas and should be maintained regularly. Public stairways with high traffic areas should be maintained more often. Anyone walking up and down the stairways should notify the building owner of any problems, to prevent accidents in the future.