CAT 40 and CAT 50 are steep taper tool holders that pull into the spindle by a pull stud. CAT 40 fits most vertical machining centers. CAT 50 is the stiffer size for heavy cutting. HSK uses a short hollow taper that clamps from the inside and seats on taper and face, which suits high spindle speeds.
How a CAT Holder Works
CAT holders use a 7/24 steep taper with a V-flange that the tool changer grips. A pull stud threads into the back of the holder, and the drawbar in the spindle grabs it and pulls the taper tight. The number is the taper size. A CAT 40 taper is 1.75 inches across at the gauge line and a CAT 50 is 2.75 inches, so a 50 taper holder is a much heavier piece of steel.
Pull studs are not universal. Machine builders use different pull stud styles, so always match the stud to the spec in the machine manual. A wrong pull stud can let a holder come loose in the spindle. Everything we have in stock is in our tooling and tool holders category.
CAT 40: The Common Size
CAT 40 is what most vertical machining centers run. It handles the bulk of everyday milling, drilling and tapping, and the holders are light enough to change fast. We carry CAT 40 3/4 inch end mill holders, CAT 40 1/2 inch end mill holders and CAT 40 1-1/4 inch end mill holders, plus a CAT 40 dead center.
CAT 50: Heavy Cutting
CAT 50 shows up on larger verticals, horizontals and machines built for heavy stock removal. The bigger taper is stiffer, so it handles big face mills, long boring bars and heavy roughing with less chatter. The trade off is weight. A 50 taper tool changer is usually slower, and the holders are harder to handle by hand.
Our CAT 50 tool holders include Lyndex and Sandvik pieces. We also have a Parlec C50 holder, Valenite CAT 50 collet holders, face mill holders from Parlec and Sandvik, and Valenite CAT 50 boring bars.
BT Is Not CAT
BT holders use the same steep taper, but the flange and pull stud thread are different. A BT holder and a CAT holder are not interchangeable even when the taper number matches. Check which one your machine takes before you buy. We have a BT50 tool holder listed for machines that run BT.
HSK: Built for Speed
HSK is a different design. The shank is short and hollow, with a shallow taper. Clamping parts inside the spindle grip the holder from the inside, and that grip holds up well at high RPM. The holder seats on both the taper and the flange face, which gives good stiffness and repeatable tool length. That is why HSK is common on high speed machines and on many European builders.
The number in the name is the flange diameter in millimeters, so HSK 63 is a 63 mm flange and HSK 100 is a 100 mm flange. The letter is the form. HSK-A is the common form for automatic tool change. Our HSK stock includes Nikken HSK100A end mill holders, HSK100A collet chucks from Showa and Nikken, a Hertel HSK 63 holder and an Xactform HSK100.
Which One You Need
Your spindle decides it. You cannot put an HSK holder in a CAT spindle or a 50 taper holder in a 40 taper machine. If you are buying a used machine, check the spindle taper first, then build tooling around it. Our used CNC machines include a Samsung MCV 50 vertical machining center with a FANUC 0i control. Check the listing for its spindle taper before you order holders.
Checking Used Tool Holders
- The taper. Look for fretting, rust, dings and polished bands. A damaged taper will not seat right and will hurt runout.
- The flange. Check the drive slots and the V groove where the tool changer grips. Chipped flanges can cause tool change problems.
- Threads. Look at the pull stud thread and any clamping screws.
- Clamping style. Match the holder to the work. Sandvik hydraulic tool holders and the Sandvik Hydrogrip grip a straight shank evenly for finishing work.
- Regrinding cutters. If you are building a tool crib, a CNC tool and cutter grinder like our Oerlikon B10 keeps end mills and drills in service.
Related Guides
- Boring heads and boring bars explained
- Building a tooling package
- Used vertical machining center checklist
Selling Tool Holders or a Whole Crib?
We buy tooling along with the machines it came off, from a few holders to a full plant. Use our sell your tooling and machinery page, or ask about tooling appraisals for a large crib.
Need a holder in a specific taper? Call 586-752-0090, extension 1 for sales, or send our sales team a note.