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Gage Block Accessories

Guide · Updated October 27, 2026

A box of gage blocks is only half of a precision kit. Holders, jaws, scribers, a stone, an optical flat and a decent case turn loose blocks into inside and outside gauges, height masters and layout tools, and they keep the blocks accurate for longer. Here's what each accessory does and which ones are worth buying.

Build the stack first

Every accessory setup starts with a stack. Get the fewest-block combination from the free Gage Block Calculator. Free, no login.

Holders, tie rods and base blocks

A holder clamps a long stack so you can handle it without breaking the wring. Tie rods carry longer builds, and a base block stands a stack upright on the surface plate. Clamp gently: too much force bows the stack.

Jaws: inside and outside sizes

Pairs of flat and half-round jaws wrung on the ends of a stack make a snap gauge (outside size) or an inside gauge for setting bore gauges and checking caliper inside jaws. Add the jaw sizes into your stack math. Then build the stack for whatever is left.

Scriber and center points

A scriber point on top of a stack in a base block makes a precise layout height. A center point lets you scribe arcs from a known radius. Both turn the gage block set into a height master. To check the height gage itself, see how to check a height gage.

Gage block stone

A fine, dead-flat stone removes raised burrs that stop blocks wringing. Clean both the stone and the block, then slide the block lightly across the stone with no pressure, wiping and checking as you go. It takes off high spots, not size. More in gage block care.

Optical flat

An optical flat shows the flatness of a block face as interference bands. Under monochromatic (helium) light each band is about 11.6 µin (0.29 µm). Straight, evenly spaced bands mean the face is flat. Curved or ringed bands point to a burr, wear or a domed face. A flat also lets you check micrometer anvils. Full method: how to use an optical flat.

Cases and protection

Keep the fitted case closed, use a thin rust preventive on steel blocks in humid shops, and store blocks apart, never wrung together. Ceramic blocks skip the rust problem; see carbide vs steel vs ceramic.

How to set up a stack in a holder

Clean the blocks and accessories: Wipe the blocks, jaws and base with a lint-free cloth and solvent, then let everything reach room temperature.
Build and wring the stack: Build the fewest-block stack for the size you need and wring it, thickest blocks first.
Add the jaws or points: Wring the jaws, scriber or center point onto the ends of the stack.
Clamp gently in the holder: Seat the stack in the holder and tighten just enough to hold. Too much clamp force can bow the stack.
Check and use: Confirm the size, use it for your check, then take it apart, clean and protect every face.

What to buy first

Home shop: a stone and a good case. Add a small accessory set later.
Toolroom: a full accessory set with jaws, scriber, base and holders, plus carbide wear blocks.
Inspection: add an optical flat and a monochromatic light.

FAQ

What comes in a gage block accessory set?

Usually a holder or clamp with tie rods, a base block, pairs of flat and half-round jaws, a scriber point and a center point. With them you can turn a wrung stack into an inside or outside size, a height gage or a layout scriber.

What is a gage block stone used for?

A flat, fine stone (often ceramic, granite or hard Arkansas) for removing raised burrs and nicks from gage block faces so they wring again. It takes off high spots without changing the size of the block.

How do you check a gage block with an optical flat?

Wring or rest the clean flat on the clean face, look under monochromatic light, and count the interference bands. Straight, parallel bands mean a flat surface; each band is about 11.6 microinches (0.29 µm) under helium light.

Do I need accessories to use gage blocks?

No. Most shop work only needs the blocks, a clean surface plate and a micrometer or indicator. Accessories pay off once you check inside sizes, set height gages or do layout from a stack.

Is there a free calculator for the stack inside a holder?

Yes. The Gage Block Calculator at gageblockcalc.com finds the fewest-block stack for inch and metric sets. Remember to account for jaw sizes when building an inside or outside size.

Related guides and calculators

Build your stack in seconds

The free Gage Block Calculator finds the fewest-block combination for inch and metric sets, with wear blocks. No login.

Questions? Ask a machinist.

General shop information only — follow your gage manufacturer's instructions and your quality system.