This category contains sites of machine shops -- and there are relatively few of them -- that concentrate on what is perhaps the same idea: the drilling of centered holes through lengths of tubing, and usually long ones at that. Gundrilling, as its name suggests, originated as an operation in the manufacture of firearms, but it now applies to various other deep hole drilling applications. Boring -- in the case of this category at least -- applies to the creation of large diameter rings, invariably with quite thick walls. And trepanning is a process that produces thick walled tubes in such a way that the centre core is retained rather than being drilled away (as, in contrast, it is in gundrilling and boring operations).

Note: Although some shops include one or more of the capabilities covered in this category, their sites need to be focused on them to be listed here. If the business emphasis lies elsewhere, the firm should be indexed in a correspondingly more appropriate category.