Measuring a 0.6250 in bore at ±0.0002 in in 6Al‑4V tubes with about 0.040 in wall, and my dial bore gage swings 0.0003 in from grip/angle. What tool repeats within 0.0001 in on thin-wall Ti at about 68°F — air gage, 3‑point electronic, or a specific contact kit?
@OP I’d go with a two‑jet air plug (Federal/Mahr) set on a 0.6250 class X ring at 68°F; it’ll repeat within 0.0001 and won’t give the bore a gorilla‑handshake squeeze. Just keep clean, regulated air and a certified ring master; if you must go handheld, a Mitutoyo 468 low‑force Holtest with thin‑wall anvils can work but expect a touch more scatter. Do you have a ring master and air at the bench?
For 0.040 in wall Ti, 3‑point heads will egg the bore; I’ve had ±0.00005 in repeat with a low‑force 2‑point comparator (Mahr 844 with thin‑wall anvils) and a torque‑limiting handle. Nest the tube in a split Delrin sleeve and set the gage on a 0.62500 master at 68°F; that kills the 0.0003 in swing from grip/angle. If you’d rather follow @nathan_bell34’s air route, keep line pressure low and use a support sleeve so the jets don’t balloon the tube.