Welding Table Hole Patterns: 5/8 Inch vs 16 mm Accessory Fit

A 5/8 inch hole is about 15.9 mm and a 16 mm hole is 16 mm, so the two are close but not identical, and spacing and plate thickness can differ too. A 5/8 inch pin should drop into a 16 mm hole, while a 16 mm pin will not fit a true 5/8 inch hole. Measure your table and the accessory listing before you buy, and treat vague compatibility claims with caution.

Why hole systems matter

Many fabrication tables have a grid of precision holes that accept pins, stops, clamps and squares. The holes let you build a fixture that is repeatable, square and fast to reset. That only works if every accessory fits every hole, which is why the diameter, the spacing and the plate thickness all matter.

At least three hole systems are sold, and they are not interchangeable by default: an imperial 5/8 inch system, a 16 mm metric system and a larger metric system built around a bigger hole. Our guide to what makes a good welding table covers the rest of the table, and the best welding tables roundup compares tables.

5/8 inch versus 16 mm: the arithmetic

A 5/8 inch hole is 0.625 inch, or 15.875 mm. A 16 mm hole is 16 mm, or about 0.630 inch. The difference is about 0.125 mm, a few thousandths of an inch. It sounds trivial, but it decides which way the accessories swap.

• A 5/8 inch pin in a 16 mm hole: it should fit, with slightly more play than the system was designed for. One table maker's FAQ calls the two sizes “theoretically interchangeable” and says a 5/8 inch tool will fit any hole made for a 16 mm tool.
• A 16 mm pin in a 5/8 inch hole: on paper it is larger than the hole, so it will not seat without forcing it. Do not file, hammer or ream pins to make them fit.
• Real-world tolerance: actual pins and holes are made to tolerances the table maker sets, and you should not assume either size is exact. Ask the seller what tolerance they claim.

The same FAQ says there is no industry standard for fabrication tables with 16 mm holes. That is a seller’s statement, not a standards finding, but it matches the general advice below: confirm, do not assume.

Spacing and plate thickness

Diameter is only the first check. Spacing between hole centers decides whether a fixture with two pins lines up with two holes. One maker lists a 2 inch grid for its 5/8 inch tables and a 50 mm grid (listed as about 2 inch) for its older 16 mm line, and a 100 mm grid for a 28 mm hole system.

A 2 inch grid and a 50 mm grid are close, but they are not the same: 50 mm is 1.9685 inches, so the gap grows by about 0.031 inch per hole. Over a pair of pins three holes apart, the mismatch is roughly 0.09 inch, which is enough to bind a fixture. Treat that as a reason to check each accessory's spacing, not a claim that every pair is incompatible.

Plate thickness is the third factor. Pins, stops and clamps are made for a particular top thickness, and the same maker lists very different top-plate thicknesses across its table lines. A tool designed for a thick top may not clamp properly on a thin one. Ask the seller for the plate thickness and the pin or shank length.

Reading compatibility claims

Accessory sellers often state that their fixtures fit tables from any manufacturer with the same hole size. One maker of 16 mm tooling says exactly that for its own line. Treat it as the seller’s claim and check the details yourself.

• Does the listing state the pin diameter in mm or inches, and does that match your hole?
• Does it state the grid spacing it is designed for?
• Does it state the plate thickness range it suits?
• Does it state a load rating, and is it the rating for the tool or for the table?
• Can you return it if it does not fit?

Before you buy, check with the seller if the answers are not listed. Marketplace listings are often vague, which is where a quick message saves a return.

How to measure your own table

1. Measure the hole diameter with calipers at several holes, since wear and coatings change the numbers. Record the result in mm and inches.
2. Measure center to center across several holes in a line, not between two neighbors, and divide by the count. That averages out small errors.
3. Measure the plate thickness at an edge or through a hole.
4. Check the table's documentation. If the maker names the system, use that name when you search for accessories.
5. Test one pin first. Buy a single pin or clamp, check the fit, then buy more.

If you only need clamping without a grid, our guide to welding clamps and magnets and clamps roundup cover options that do not depend on a hole pattern.

Buying a table or adding to one

If you are choosing a table, pick the hole system before you buy accessories, not after. Check that the system has the accessories you want and a choice of suppliers. Ask which system has the accessories and suppliers you can actually reach where you live. Whichever you choose, keep a note of the grid, hole size and plate thickness with the table’s paperwork. Our tool storage article has ideas for keeping fixtures and pins organized once you own them.