Are Used CAT40 Tool Holders Worth Buying? How to Check Them

Used CAT40 holders show up everywhere: in shop cleanouts, in auction lots, and in the box that comes with a used machining center. Some are fine for years of work. Others will put runout and chatter into every part and can mark up your spindle taper. The difference is usually visible in a few minutes if you know where to look. This guide covers what to check before you pay for them or load one into your spindle.

Print this checklist

First, make sure it really is CAT40

CAT40 and BT40 share the same 7/24 taper angle but are not interchangeable. The flange, the drive slots and the retention-knob thread are different (CAT40 uses a 5/8-11 inch thread, BT40 uses M16). A BT40 holder in a lot labeled “40 taper” is a common surprise.
Look for the orientation notch on the flange and confirm it matches what your tool changer expects.
Check whether a holder is dual-contact (face and taper) and whether your spindle is built for that. Ask the spindle builder if you are not sure how the two mix on your machine.

The taper: fretting, nicks and contact

Fretting. Rust-brown or dark bands or patches on the taper come from tiny movement between holder and spindle. It means the holder was not seating tight, and it often comes with runout. Light staining that wipes off is different from pitted, etched bands.
Nicks, dings and raised burrs. Run a clean fingertip and a light along the full taper. A raised burr can transfer damage to your spindle taper. Do not load a holder with a burr you can feel.
Contact pattern. If you have a taper ring gage, a light coat of bluing shows where the holder actually touches. Contact concentrated at one end, or in patches, means the taper is worn or damaged.
Crash marks. A bent nose, a cracked flange or chewed drive slots usually means the holder was in a crash. Treat it as scrap, not a bargain.

Runout: measure it, don’t guess

Check runout (TIR) in a spindle you trust, or in a holder setup fixture, with a clean taper and a clean holder.
Indicate at the nose of the holder and again out at working length on a ground test bar or a known-good gage pin. Runout that grows a lot with length points to a bent holder, a worn bore or a bad collet.
For collet chucks, test with a new collet before you blame the holder. Worn collets and damaged nut threads cause a lot of “bad holder” complaints.
Compare the reading with what the work needs. A holder that is fine for drilling may not be good enough for a finish end mill or a reamer.

Pull studs: plan on new ones

Pull studs (retention knobs) are wear parts, and they are what keeps the holder in the spindle. Used ones with an unknown history are a poor place to save money. Many shops replace them on every used holder they bring in.
CAT40 pull studs are not all the same. Machine builders specify different angles and lengths, and through-coolant holders need a through-hole stud. Use the stud your machine builder specifies, torqued to their spec.
Look at the stud threads inside the holder. Damaged or galled threads in the holder can make it unusable.

Checks by holder type

Collet chucks (ER and similar)

Check the nut threads and the collet taper inside the body for dings and wear. Bring a new collet to test with.

End mill and side-lock holders

Check the bore for galling and the set-screw threads. A bore that has been run with an undersize tool can be bell-mouthed.

Hydraulic holders

Make sure it clamps and releases and holds a gage pin firmly. A leaking or soft holder usually needs to go back to the maker for service, so price that in.

Shrink-fit holders

Check the bore for scoring, and look for damage from overheating. Make sure you have, or can use, a shrink machine that fits them.

Shell mill and face mill arbors

Check the pilot diameter, the drive keys and the face for dings. A damaged face means the cutter will not run true.

Coolant-through holders

Check that the coolant passage is clear and any seals are present. They need a matching through-coolant pull stud.

Balance and high speed

Most used holders come with no balance record. For general work at moderate speeds that is often fine. If you run high spindle speeds, treat unknown balance as a risk, and consider having holders checked before you rely on them at the top of the speed range.

Buying a lot of used holders

Ask for close, lit photos of the taper on each holder, not just a group photo of the rack.
Ask what machine they came out of and whether they were in use until it was taken down.
Ask whether pull studs and collets are included, and price new ones in anyway.
Sort on arrival: good, needs a check, scrap. Count only the good pile when you decide what the lot was worth.
Holders that come with a used machine: count only holders that are in good shape and fit that spindle (see the used machining center checklist).

Selling holders or a tooling package?

Holders, collets and tooling packages can go through Used CNC Tooling. Send the taper, the holder types, quantities and a few close taper photos. Holders that go with a machine you are selling belong in the machine listing; see how to prepare a machine for sale. Worn-out solid carbide end mills and drills can go to Machine Shop Scrap.

Used CAT40 holder FAQ

Are used CAT40 tool holders worth buying?

Often, if the taper is clean with no fretting or burrs, runout checks out at the nose and at working length, and you plan on new pull studs. Skip holders with crash damage, pitted fretting or damaged threads.

Can a BT40 holder go in a CAT40 spindle?

No. They share the taper angle, but the flange, drive slots and retention-knob thread are different. Check what you are buying before it gets near your tool changer.

Should I reuse the pull studs on used holders?

Many shops replace them. Pull studs are wear parts that keep the holder in the spindle, and they are inexpensive compared with the risk. Use the stud your machine builder specifies.

What does fretting on a tool holder mean?

Brown or dark marks on the taper from small movement between holder and spindle. It means the holder was not seating tight, and pitted fretting usually comes with runout. Check the spindle taper too.

How do I check runout on a used holder?

In a clean spindle or holder setup fixture, indicate at the nose and again at working length on a ground test bar or gage pin. For collet chucks, test with a new collet first.