These are the Starrett Mechanical Digital Depth Micrometers — simple to use even by the inexperienced.

• Clear, easily read white numbers on black background reduce errors
• No-glare black finish on the frame
• .001" or 0.01mm is read directly from the counter
• Ring-type knurled lock nut for quick and sure locking
• Combination ratchet and speeder for uniform pressure and quicker adjustment
• Hardened, ground, and lapped base is 3" (75mm) long
• Measuring rods are 5/32" (4mm) diameter and are adjustable