The Morse Taper is the most widely used self-holding taper system in metalworking. Developed by Stephen Morse in the 1860s, this elegantly simple design uses a shallow conical interface to lock cutting tools into machine spindles through friction alone — no chuck, no drawbar, no clamping mechanism. Over 160 years later, the same basic geometry remains the global standard for drill presses, engine lathes, and radial arm drills.
This guide provides the complete technical reference for Morse Taper sizes MT0 through MT6, with specific focus on the MT1–MT5 range used for taper shank twist drills (DIN 345). Whether you are specifying drills for a new machine, selecting adapter sleeves, or training operators on proper insertion technique, this is the reference you need.
What Is a Morse Taper?
The Principle: Self-Locking Through Geometry
A Morse Taper is a precision-ground conical surface with an included angle of approximately 2.98 degrees (about 1.49 degrees per side). This is deliberately shallow — shallow enough that when the male taper (on the drill shank) is pushed into the female taper (the machine spindle bore), the two surfaces wedge together and lock through friction.
The physics behind this are straightforward: at taper angles below approximately 8.5 degrees (the critical self-holding angle for steel-on-steel), the friction force between the mating surfaces exceeds the component of axial force that would tend to push them apart. The result is a joint that gets tighter under load — the harder you push the drill into the work, the more securely the taper grips.
This self-locking property is what distinguishes Morse Tapers from steep-taper systems (like BT, CAT, and HSK tool holders in CNC machines), which have taper angles of 3.5 degrees per side or more and require a mechanical drawbar to hold the tool in place.
Key Components
- Taper surface: The precision-ground conical surface that provides the friction grip. Surface finish is critical — any contamination, oil, or damage drastically reduces holding force.
- Tang: A flat tab at the small end of the taper that fits into a cross-slot in the spindle bore. The tang serves two purposes: it acts as a safety backup against rotation (the primary torque transmission is through the taper friction), and it provides a surface for the drift key to push against when ejecting the tool.
- Drift slot: An elongated opening in the side of the machine spindle bore that allows a tapered wedge (drift key) to be inserted to push the tang — and thus the entire drill — out of the bore.
Historical Context
Stephen Morse patented the taper system in 1864 while working as a machinist in New Bedford, Massachusetts. The original Morse Twist Drill and Machine Company defined seven taper sizes (MT0 through MT6), and these dimensions have remained essentially unchanged for over a century. The system is now codified in international standards including DIN 228 (German), ISO 296 (international), and ANSI B5.10 (American). All three standards define the same physical dimensions — a DIN 228 MT3 is identical to an ISO 296 MT3.
MT Size Dimensions Table (MT0–MT6)
The following table provides the key dimensions for all seven standard Morse Taper sizes. MT1 through MT5 are the sizes relevant for taper shank twist drills (DIN 345). MT0 is used for small tooling and accessories. MT6 is found on large machine spindles but is rarely used for standard twist drills.
| MT Size | Large End Diameter (D) | Small End Diameter (d) | Taper per Foot | Taper Length (mm) | Tang Thickness (mm) |
|---|---|---|---|---|---|
| MT0 | 9.045 mm | 6.401 mm | 0.6246 in/ft | 49.8 | 3.9 |
| MT1 | 12.065 mm | 9.371 mm | 0.5986 in/ft | 53.5 | 5.2 |
| MT2 | 17.780 mm | 14.533 mm | 0.5994 in/ft | 64.0 | 6.3 |
| MT3 | 23.825 mm | 19.761 mm | 0.6024 in/ft | 80.5 | 7.9 |
| MT4 | 31.267 mm | 25.908 mm | 0.6233 in/ft | 102.5 | 11.9 |
| MT5 | 44.399 mm | 37.467 mm | 0.6315 in/ft | 129.5 | 15.9 |
| MT6 | 63.348 mm | 53.746 mm | 0.6257 in/ft | 182.0 | 19.0 |
Notes on the table:
- The taper per foot varies slightly between MT sizes — Morse Tapers are not a single uniform taper ratio. This is a common misconception. Each MT size has its own specific taper angle.
- The large end diameter (D) is the dimension that determines the maximum bore diameter the spindle must have to accept the taper.
- Taper length is the usable contact length of the conical surface, not including the tang.
Drill Diameter to MT Assignments (DIN 345)
The DIN 345 standard assigns specific Morse Taper sizes to each drill diameter. The assignment is based on the torque requirements at each diameter — larger drills need larger tapers to transmit the necessary torque without slipping. The transition points are standardized and recognized worldwide.
| Morse Taper | Drill Diameter Range | Typical Diameters (DIN 345) | Transition Drill Diameter |
|---|---|---|---|
| MT1 | 6.0–13.8 mm | 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 13, 13.5, 13.8 | Starts at 6 mm |
| MT2 | 14.0–23.0 mm | 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, 20.5, 21, 21.5, 22, 22.5, 23 | Transitions at 14 mm |
| MT3 | 23.2–31.5 mm | 23.5, 24, 24.5, 25, 25.5, 26, 26.5, 27, 27.5, 28, 28.5, 29, 29.5, 30, 30.5, 31, 31.5 | Transitions at ~23.2 mm |
| MT4 | 32.0–50.0 mm | 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 | Transitions at 32 mm |
| MT5 | 51.0–76.0 mm | 51, 52, 53, 54, 55, 56, 58, 60, 62, 63, 65, 68, 70, 72, 75, 76 | Transitions at 51 mm |
Key observations:
- The transition points (where the MT size steps up) are well-defined: 6 mm (MT1), 14 mm (MT2), ~23 mm (MT3), 32 mm (MT4), 51 mm (MT5). These boundaries are based on torque calculations — the taper must provide sufficient friction area to handle the drilling torque at the maximum diameter in its range.
- Within each MT range, half-millimeter increments are available for most sizes, though not all are commonly stocked. Standard diameters (whole numbers and 0.5 mm increments) are far more readily available than odd sizes like 13.3 mm.
- The MT assignment is fixed by the standard — a 20 mm DIN 345 drill always has an MT2 taper, regardless of the manufacturer.
Taper Sleeve Adapters (DIN 2185)
A taper sleeve (also called a reduction sleeve or adapter sleeve) allows you to use a drill with a smaller Morse Taper in a machine with a larger Morse Taper spindle. The sleeve has a female taper (matching the drill) on the inside and a male taper (matching the spindle) on the outside. Taper sleeves are standardized under DIN 2185.
Standard Sleeve Combinations
| Sleeve Designation | Inside (Drill MT) | Outside (Spindle MT) | Common Use Case |
|---|---|---|---|
| MT1 → MT2 | MT1 | MT2 | Using 6–13 mm drills in an MT2 drill press or lathe tailstock |
| MT1 → MT3 | MT1 | MT3 | Small drills in a floor-standing drill press with MT3 spindle |
| MT2 → MT3 | MT2 | MT3 | 14–23 mm drills in an MT3 machine — very common combination |
| MT2 → MT4 | MT2 | MT4 | Medium drills in a radial arm drill press |
| MT3 → MT4 | MT3 | MT4 | 24–31 mm drills in an MT4 radial drill — very common |
| MT3 → MT5 | MT3 | MT5 | Medium drills in large radial drills |
| MT4 → MT5 | MT4 | MT5 | 32–50 mm drills in large MT5 machines |
Important Rules for Taper Sleeves
- One sleeve maximum is the professional standard. While stacking two sleeves (e.g., MT1→MT2 inside MT2→MT4) is physically possible, each sleeve adds runout (typically 0.01–0.03 mm per sleeve) and reduces rigidity. For precision work, never stack sleeves.
- The sleeve tang must engage the spindle drift slot. When using a sleeve, the sleeve's tang (not the drill's tang) is what engages the spindle bore's drift slot. The drill's tang engages the internal slot of the sleeve.
- Clean all taper surfaces before assembly. The sleeve, drill taper, and spindle bore must all be wiped clean of oil, coolant, and chips. Contamination between any mating surface reduces grip and introduces runout.
- Ejection requires two steps: First, use the drift key through the spindle slot to push out the sleeve (with the drill still inside it). Then, use a smaller drift key to push the drill out of the sleeve. Never try to eject the drill directly through the spindle slot when a sleeve is in use — the geometry does not align.
How to Insert & Eject Taper Shank Drills
Proper Insertion Technique
- Clean both surfaces. Wipe the drill taper and spindle bore (or sleeve interior) with a clean, lint-free cloth. Remove all traces of oil, coolant, and metal chips. Even a thin film of oil can reduce holding force by 40–60%.
- Align the tang. Rotate the drill so the tang aligns with the drift slot in the spindle bore (or the tang slot in the sleeve). The tang should slide into the slot as the taper enters the bore.
- Push firmly by hand. Insert the taper into the bore and push firmly. For most sizes up to MT3, hand pressure is sufficient to seat the taper. You should feel the taper engage and resist further pushing.
- Seat with a sharp tap (if needed). For larger MT sizes (MT4, MT5) or for a tighter grip, give the end of the drill a sharp tap with a soft-faced mallet (copper, brass, or dead-blow hammer). One firm tap is sufficient. Do not use a steel hammer — it will damage the drill end and mushroom the tang.
- Verify the seat. Try to rotate the drill by hand — it should not move. There should be no visible gap between the end of the taper surface and the face of the spindle bore. If the drill rocks or has visible runout, eject it, inspect both surfaces for contamination or damage, and reinsert.
Proper Ejection Technique (Drift Key Method)
- Select the correct drift key. The drift key (also called a drill drift) is a tapered, flat steel wedge. It must fit through the drift slot in the spindle and contact the edge of the tang. Using an undersized drift can damage the slot; using an oversized drift will not fit.
- Insert the drift key through the slot. Push the tapered end of the drift key through the elongated slot in the spindle bore until it contacts the end of the tang.
- Strike the drift key with a hammer. Give the wide end of the drift key a firm tap with a ball-peen hammer or brass mallet. The wedge action of the drift key pushes the tang (and the entire drill) axially out of the bore. Usually 1–3 taps is sufficient.
- Catch the drill. As the taper breaks free, the drill will drop. Always hold one hand under the drill to catch it. A large taper shank drill falling from a drill press spindle onto the table or floor can damage the cutting edges, the taper surface, or the workpiece.
- Remove the drift key. Once the drill is free, pull the drift key out of the slot. Do not leave it in place — it will interfere with the next tool insertion.
Safety Warnings
- Never use a screwdriver, punch, or bolt as an improvised drift key. These tools do not match the slot geometry and will damage the tang, the slot, or both. Use a proper drift key sized for your spindle.
- Never hammer the drill directly to seat it. Striking the cutting end or flutes of a drill will damage the cutting edges and can crack heat-treated HSS. Always strike the shank end or use a soft mallet on the drill's flat end.
- Never run the spindle to "tighten" the taper. The taper seats through axial force, not rotation. Running the spindle with a loosely inserted drill can cause the drill to fly out.
Taper Surface Maintenance & Care
The performance of the entire Morse Taper system depends on the condition of the taper surfaces. A damaged or contaminated taper will slip, chatter, produce oversize holes, and can be dangerous. Regular maintenance is simple but essential.
Cleaning
- Wipe taper surfaces clean before every insertion. Use a lint-free cloth or paper towel. For stubborn residue, use acetone or isopropyl alcohol — never use WD-40 or machine oil on taper surfaces that need to grip.
- Clean the spindle bore after every ejection. Use a bore cleaning cloth or a wooden dowel wrapped in clean cloth. Chips and coolant accumulate in the bore and must be removed.
- Inspect taper surfaces visually before insertion. Look for nicks, burrs, scoring, or discoloration (which may indicate overheating).
Oiling for Storage
When storing taper shank drills for extended periods, apply a thin film of light machine oil or rust-preventive oil to the taper surface. This prevents corrosion. Important: always wipe the oil off completely before using the drill. Oil on the taper surface is the most common cause of slipping.
Repairing Minor Damage
- Small nicks or raised burrs: Carefully stone with a fine India stone or fine-grit diamond file. Work along the taper axis (lengthwise), never across it. The goal is to remove the raised material without creating a flat spot.
- Light scoring: If scoring is shallow (you cannot feel it with a fingernail), the drill may still function acceptably. Deep scoring requires the drill to be retired from precision work — it can still be used for roughing applications where slip risk is acceptable.
- Mushroomed tang: If the tang has been damaged by repeated hammer strikes, carefully file or grind it back to the original profile. A mushroomed tang will not fit into the drift slot and makes ejection difficult.
Spindle Bore Maintenance
The spindle bore is harder to service than the drill taper, and damage to the bore affects every tool used in that machine. Preventive care is far cheaper than repair:
- Never leave a drill in the spindle when not in use — temperature changes can cause the taper to seize.
- Periodically check the bore for bell-mouthing (enlarged opening) by inserting a gauge plug or a known-good taper shank and checking for wobble.
- If the bore is damaged, it can be restored with a Morse Taper reamer sized for the specific MT. This is precision work and is best performed by a qualified machine tool technician.
Zhonghuan manufactures a complete range of DIN 345 taper shank HSS twist drills from MT1 (6 mm) through MT5 (76 mm) in both M2 and M35 steel grades. All tapers are precision ground and inspected against DIN 228 gauge standards. Contact us for bulk pricing or custom specifications.
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