Inxens Drill Bit Depth Stop Collars, 8 Metric Sizes 3–16 mm

What does a drill bit depth stop do?

A drill bit depth stop is a steel collar that locks onto the bit with a set screw. When the collar meets the face of the workpiece, it acts as a physical stop, so every hole drilled at that setting comes out at a consistent depth. This set has eight black carbon steel collars for 3, 4, 5, 6, 8, 10, 12 and 16 mm bits, plus a small L-shaped hex key for the set screws. Drill bits are not included.

Which collar fits which drill bit?

Each collar has a fixed, labeled inner diameter; only its position along the bit is adjustable. Pick the collar that matches the bit's diameter.

There is no 9 mm or 14 mm collar in this set.

Can you use metric collars on inch drill bits?

Only where an inch bit is at or just under a metric size. A 5/32 in bit (3.97 mm) is a near match for the 4 mm collar. A 1/4 in bit measures 6.35 mm, so it won't pass through the 6 mm collar and sits loose in the 8 mm one, where the set screw would push it off center. If most of your bits are fractional-inch sizes, an inch-sized collar set is the better match.

How to set the depth

1. Decide on the depth, measured from the cutting tip of the bit. For dowel joints, a common rule of thumb is half the dowel length in each piece plus 1 to 2 mm so glue has room.
2. Slide the matching collar onto the bit and line up its lower face with your depth mark, using a ruler or a marked block.
3. Tighten the set screw with the hex key until it's snug, then try to slide the collar by hand. If it moves, snug it a little more. Don't overtighten.
4. Drill a test hole in scrap, measure it, and adjust before you drill the workpiece.

On a twist bit, a set screw that lands in a flute groove may not grip well. Turn the collar slightly so the screw bears on the raised spiral, then recheck the depth.

Slow down as the collar reaches the surface and stop when it touches. A spinning steel collar pressed hard against wood can scuff it, and repeated contact can work the set screw loose over a long batch, so recheck the collar now and then.

Collar or a flag of tape?

A flag of tape wrapped around the bit is a quick visual depth marker, and a roll of black, red and white electrical tape does that job in a pinch. Tape only shows you where to stop, though. A locked collar gives a physical stop, which matters when you're drilling a long row of shelf-pin holes or matching dowel holes in two boards. Either way, a depth stop is an aid, not a substitute for careful drilling.

Who it's for, and care

The set suits woodworkers and DIYers doing dowel joinery, shelf-pin layouts and batches of pilot holes with metric bits. Skip it if you need inch sizes or a 9 or 14 mm collar. Wipe the collars clean and dry after use and store them away from moisture, since carbon steel can rust if it stays damp. More workshop basics are in tools and hardware.