Indicators are sold with lug backs, flat backs or both. Lug backs are a good way to mount indicators on most truing stands. As an example they make for drop-in replacements on Park Tool TS-2/3/4 truing stands. Flat backs are an alternative if you plan to mount indicators by their stems and want to keep the rear tidy. Magnetic indicator mounts and most tensiometers use a stem clamp design.
iGaging indicators include both styles so you can switch back and forth. Mitutoyo indicators are sold as one style or the other, however you can purchase extra backs to convert a flat back to a lug back or vice versa. By Mitutoyo part numbering conventions, models numbers ending in the letter ‘B’ ship with flat backs. Model numbers not ending with ‘B’ ship with lug backs.