The X-Acto knife may be called a utility knife, but it is actually a short, sharp blade mounted on a pen-like aluminum body, used for crafting and hobbies, such as modelmaking. Before the availability of digital image and text processing tools, preparing camera-ready art for use in printing (literal cut and paste or paste up) depended heavily on the use of knives like the X-Acto for trimming and manipulating slips of paper.
The knife shown is the most common type, fitted with the usual "Number 11" blade. It is 5 3⁄4 inches (145 mm) overall. The knurled collar loosens and tightens an aluminium collet, which holds the replaceable blade.
There are numerous other knives on the market with very similar designs, and blades are typically interchangeable between different brands.
The original knife was invented in the 1930s by Sundel Doniger, a Polish immigrant to the United States. He had planned to sell it to surgeons as a scalpel but it was not acceptable, because it could not be cleaned. His brother-in-law, Daniel Glück (father of Louise Glück, the poet), suggested that it might be a good craft tool.