Two side-lock shanks, two flats, and a mistake that happens in real shops: putting a whistle notch cutter into a Weldon holder, or the reverse. They are close enough to fit and different enough to matter.
Need a holder for either shank? Mongtec end mill holders are made in both forms — Weldon (DIN 1835-B) and whistle notch (DIN 1835-E), bores 6 to 50 mm, on BT and BBT tapers. Ask for a quote.
| Weldon, DIN 1835-B | The flat is parallel to the axis. The set screw pushes sideways onto the flat. Axial position is set by how far you push the tool in. |
|---|---|
| Whistle notch, DIN 1835-E | The flat is inclined — Mongtec cuts it at 2°. As the screw tightens it also pulls the tool back against the seat, so the axial position is defined by the holder, not by the operator. |
Whistle notch cutter in a Weldon holder: the screw contacts the inclined flat on one edge only. Contact area collapses, the screw can mark the shank, and the tool can creep out under axial load.
Weldon cutter in a whistle notch holder: the screw pushes on a parallel flat with no pull-back effect. It will hold for light work, but you lose the axial repeatability that is the reason for choosing a whistle notch in the first place.
Use Weldon for roughing, heavy side loads, and anywhere you want the simplest possible connection. It is the most common shank on the shop floor.
Use whistle notch when the axial position matters between tool changes — step drilling, depth-critical pocketing, or anywhere a tool creeping out by a tenth of a millimetre would scrap the part.
| Weldon | ø6 to ø50 mm on BT, BBT and HSK-A tapers. Coolant-through version available — the article number ends in K. |
|---|---|
| Whistle notch | ø6 to ø40 mm, flat at 2°. |
| Set screws | One screw up to ø20 mm; two screws from ø25 mm upward. |
Put a straight edge along the flat. If it sits flush along the whole length, it is Weldon. If it lifts at one end, it is a whistle notch. Send us a photograph if it is borderline — we would rather check than have you receive the wrong holder.
| Shank | HSS cutters | Solid carbide cutters |
|---|---|---|
| Plain cylindrical | DIN 1835-A | DIN 6535-HA |
| Weldon (parallel flat) | DIN 1835-B | DIN 6535-HB |
| Whistle notch (inclined flat) | DIN 1835-E | DIN 6535-HE |
The letter is what to check on the cutter box. A cutter marked HB or 1835-B goes in a Weldon holder; HE or 1835-E goes in a whistle notch holder. A plain HA shank has no flat at all and belongs in a collet, shrink fit or hydraulic holder, not a side-lock holder.
| Bore | Set screw | Screws |
|---|---|---|
| ø6 | M6 | 1 |
| ø8 | M8 | 1 |
| ø10 | M10 | 1 |
| ø12 | M12 | 1 |
| ø14 | M12 | 1 |
| ø16 | M14 | 1 |
| ø18 | M14 | 1 |
| ø20 | M16 | 1 |
| ø25 | M18×2 | 2 |
| ø32 | M20×2 | 2 |
| ø40 | M20×2 | 2 |
| ø50 | M24×2 | 2 |
Source: Mongtec end mill holder range. From ø25 mm the holder uses two screws, so the cutter needs two flats in the right positions — check this before buying cutters for a new holder.
Weldon and whistle notch are side-lock connections: the screw stops the cutter from pulling out, which is why they suit roughing and heavy side loads. The trade-off is run-out, because the screw pushes the shank to one side of the bore. When finish and run-out matter more than pull-out security, a collet, shrink fit or hydraulic holder is the better choice — see shrink fit, hydraulic or mechanical.
It will fit, but it should not be used that way. The screw meets the inclined flat on one edge only, the contact area collapses and the tool can creep out under axial load.
The DIN 1835-E and DIN 6535-HE flat is inclined at 2°, and Mongtec whistle notch holders are cut at 2°.
Weldon holders are built on BT, BBT and HSK-A tapers, from ø6 to ø50 mm; whistle notch holders from ø6 to ø40 mm. See Mongtec end mill holders.
Mongtec confirms fit and quotes from four details. Email them to info@mongtec.com or use the quote form — we reply within one working day.