Yes! He's using a telescoping snap gauge, which is the most common machine shop tool to measure inside diameter (ID). Inside calipers are too flexible if you want precision. I have seen sets of discs of incremental sizes, but that would be expensive for lots of discs needed. Snap gauge is just right and satisfying to use when you get the hang of it. I get bore measurements consistent within .05 mm (about 2/3 of an average human hair). I use them for studying and adjusting barrels, especially, because I can't fit the prongs of the digital caliper into the bore - and clarinet joints, to determine "large" vs. small bore.
I got a set for about $16 from Harbor Freight. Even though I only use one of them, price was right. Quality is just good enough. I see there are some on eBay too.
