Caribbean Heart Pine Knotty Unfinished Retro Stair Tread Closed 36 in

Retro treads are 3/4" thick with a 1" thick nose and traditional treads are the full 1" along the entire body. Both will look the same when installed but retro treads are used when "capping" or installing on top of an existing tread. The traditional treads are installed directly on top of the stringer and can be a standalone step. The easiest way to decide which style to use is to decide how you'll install the treads. If you intend on removing the old tread and dropping the new one in its place, use a traditional tread. If you prefer to overlay, or install something on top of the existing tread, use a retro.

These links have more information:

https://www.stair-treads.com/resources/what-are-replacement-treads.html

https://www.stair-treads.com/resources/replacement-stair-tread-information.html