THK 58cm (22.75") Linear Bearing Rail with SSR20 Bearing Blocks. Bearing blocks have four holes in a 1.25" square. The rails measure 21mm wide by 16mm tall. 

This unit has some surface rust. These are not stainless or coated and rather unforgiving to high humidity (the rust happened virtually overnight). The bearing blocks move smoothly and firmly, they could probably use a grease charge. 

Item weight is 3.58 lb.