MT2, MT3, MT4: One Machine-Fit Decision, Three Spindle Sizes
Under DIN 345, the Morse taper on a drill shank is fixed by the drill diameter: 14.25–23 mm drills carry MT2, 23.25–31.75 mm carry MT3, and 32–50.5 mm carry MT4. Nobody chooses a taper — the diameter decides it, and the machine spindle decides what seats directly and what needs a sleeve.
That is why an MT2, MT3, or MT4 search is a machine-fit search, not a generic drill search. The buyer is feeding a bench drill, pillar drill, radial drill, or lathe tailstock that uses Morse taper tooling, and already knows the interface — a much higher-intent inquiry than a general HSS drill search. For distributors, the three tapers together cover the entire 14.25–50.5 mm band that industrial channels actually stock, which is why this page treats them as one program rather than three separate products.
DIN 345 Diameter-to-Taper Map
| Taper | DIN 345 drill diameter | Typical machines | Typical holes |
|---|---|---|---|
| MT2 | 14.25–23.0 mm | Bench drills, pillar drills, lathe tailstocks | Bolt clearance M12–M20, general fabrication |
| MT3 | 23.25–31.75 mm | Radial drills, heavy pillar drills, tailstocks | Structural bolt holes M20–M30, machine-shop work |
| MT4 | 32.0–50.5 mm | Large radial drills, boring mills | Large bolt and pin holes, heavy fabrication |
Below 14 mm, DIN 345 assigns MT1 — rare in industrial programs, because most shops run straight-shank drills in a chuck at those sizes. Above 50.5 mm the standard moves to MT5 (51–76 mm); see our large Morse taper drill bits page for MT5 and DIN 1870 long patterns.
MT2 (14.25–23 mm): The Small-Spindle Workhorse
Choose MT2 drills when the machine spindle is MT2 — bench drills, smaller pillar drills, and most lathe tailstocks — or to run 14–23 mm holes in a bigger machine through an MT2-to-MT3 or MT2-to-MT4 sleeve. This band carries the bolt-clearance sizes (16, 18, 20, 22 mm) that fabrication and MRO buyers reorder constantly, which is why MT2 is the one taper that genuinely moves as a set as well as singles.
MT3 (23.25–31.75 mm): The Radial-Drill Sweet Spot
Choose MT3 when the spindle is MT3 — radial drills, heavy pillar drills, larger tailstocks — or for the 24–31.5 mm holes at the heart of structural and machine-shop work. It is the classic mid-large band: big enough to need real machine torque, common enough to move on volume.
MT4 (32–50.5 mm): Where Large-Diameter Economics Begin
Choose MT4 when the spindle is MT4 and the holes run 32–50 mm — large radial drills and boring mills doing heavy fabrication, pin holes, and big bolt patterns. From 32 mm up, the web is thick enough that point thinning (or a 130/135-degree split point) is what keeps thrust manageable, and branded per-piece prices climb steeply — exactly where factory-direct OEM supply earns its keep. For 51–76 mm and MT5, continue to the large Morse taper drill bits page.
Buyer Signals and How We Quote Them
| Buyer signal | What it means | RFQ response |
|---|---|---|
| MT number only | Buyer knows spindle taper but may not know DIN mapping | Ask for diameter list and machine type |
| MT + Dormer benchmark | Buyer wants brand benchmark and physical fit | Quote DIN 345 spec-matched sample |
| MT + steam tempered | Buyer expects dark industrial HSS finish | Confirm finish, grade, point, and packaging |
| MT + private label | Distributor or brand program | Build an assortment, not a one-off SKU |
Recommended Starter Assortment
The exact DIN 345 table should drive the final quote, but a practical distributor program usually starts from which hole sizes the customer's market repeats most. Structural steel repeats bolt clearance sizes; machine shops repeat common metric increments; MRO repeats whatever the existing machines take.
- MT2 set line: five or six DIN 345 sizes between 14 and 23 mm — the format small shops and MRO catalogs reorder.
- Core M2 line: MT3 singles in 24–31.5 mm for general steel and cast iron.
- MT4 singles: 32–50 mm for heavy fabrication accounts.
- Premium M35 line: selected sizes across all three tapers for stainless and high-tensile steel.
- Surface: steam tempered or black oxide for the industrial look; bright for some machine-shop buyers.
- Accessories: MT2-to-MT3, MT2-to-MT4, and MT3-to-MT4 sleeves, drift keys, and protective tubes.
For a full own-brand range across the tapers, see the private-label Morse taper drill bit program.
Quality Checks That Matter on Taper Shanks
- Taper seating: a poorly ground taper will not seat fully and creates runout — we verify seating contact on gauge sleeves.
- Runout at point: larger drills amplify even small eccentricity into oversize holes.
- Tang strength: the tang must survive drift ejection without deforming, on MT4 especially.
- Size marking: diameter, MT number, grade, and brand marking prevent warehouse and workshop errors.
RFQ Checklist
- Machine spindle: MT2, MT3, or MT4 direct — or larger spindle with sleeve.
- Diameter list and required DIN standard.
- Grade: M2, M35, or mixed.
- Finish: steam tempered, black oxide, bright, amber, or TiN.
- Point: 118 degree thinned or 135 degree split.
- Singles, sets, or both; accessories (sleeves, drift keys, tubes, racks).
- Branding and packaging for the buyer's channel.
Quote an MT2–MT4 Morse Taper Drill Range
Send the size list per taper, machine types, grade, finish, point, accessories, packaging, and trial quantity.
Request MT2–MT4 Quote