BMT tool holders should be selected by the complete mounting arrangement and tool position, not by the BMT size label alone. Start with the turret drawing, identify the required operation, and compare the holder's locating features, hole pitches, mounting face and cutting-tool interface. Then check the working position and clearance in the actual machine setup.
This guide uses two static holders from the local catalogue to show how to read those details. Their dimensions describe those specific configurations; they do not establish compatibility with an unnamed machine or every turret carrying the same size designation.
Start with the operation and holder type
A boring holder and an external turning holder do different jobs. The boring holder example below accepts a cylindrical tool through a specified bore. The external holder positions an external turning tool and requires its own tool-section and clamping checks. Neither example should be described as a driven holder: the local records identify both as static holders.
Before comparing dimensions, establish whether the job needs an internal boring bar or an external turning tool. Record the intended working direction, required reach and available space. A holder that fits the mounting face can still place the cutting tool incorrectly for the operation.
Read the BMT boring holder as a complete configuration
The BMT40-B25-H60 boring tool holder has the following recorded dimensions. All values in this table are millimetres.
| Feature | Drawing label | Value |
|---|---|---|
| Bore centre height | A | 60 |
| Overall front-view height | B | 83 |
| Locating-slot width | C | 12 |
| Tool bore diameter | D | 25 |
| Horizontal mounting-hole pitch | E | 50 |
| Vertical mounting-hole pitch | F | 60 |
| Mounting-face width | G | 63 |
| Mounting-face length | H | 94 |
The 25 mm tool bore and 60 mm bore centre height answer different questions. One describes the tool interface; the other describes its position. Compare each with the corresponding feature in the turret and tool drawings rather than treating a matching bore diameter as sufficient evidence of fit.
The table does not establish a particular boring bar's clamping compatibility, permissible overhang or cutting performance. Those checks depend on the actual bar, clamping arrangement and application.
Do not transfer drawing letters between holder families
The BMT40-C20-H55 external tool holder illustrates an important difference. Its drawing defines A as a 30 mm lower-step height and B as a 55 mm overall side-view height. These are not the boring holder's A and B definitions.
Its locating-slot width C is 12 mm. However, E is the 50 mm vertical mounting-hole pitch and F is the 60 mm horizontal pitch. In the boring example, E and F refer to the opposite orientations. A spreadsheet containing only letters and numbers would hide that distinction.
For the external holder, the mounting-face width G is 75 mm and the overall plan-view length H is 97 mm. Do not relabel the latter as mounting-face length: that is not what this drawing records. Retain the exact feature meaning when preparing a comparison or quotation request.
Check the mounting face, tool position and clearance
Use a short, repeatable review before selecting a configuration:
- Compare the locating-slot geometry and both mounting-hole pitches with the machine documentation.
- Check the mounting-face dimensions and the orientation shown in each drawing view.
- Match the boring-bar diameter or external tool section to the holder's documented clamping arrangement.
- Check the cutting-tool position, required reach and clearance for the intended operation.
- Obtain the applicable fastening, clamping and installation instructions before installation.
Dimensions alone do not establish allowable loads, tightening torque, coolant connections or machine-brand compatibility. Where the catalogue does not supply those details, obtain the relevant documentation instead of filling the gaps with values from a visually similar holder.
Prepare a useful BMT holder enquiry
Send the complete holder designation, machine and turret identification, and a turret-interface drawing where available. Add the cutting-tool dimensions, operation, required working position, quantity and any clearance constraints. Mark the drawing view used for each measurement so that horizontal and vertical pitches cannot be confused.
Use the tool holders and adapters catalogue to compare actual listed configurations. A family photograph or AI illustration can help explain the subject, but it cannot verify dimensions or establish that two holders are interchangeable. Base the purchase decision on the configuration record and the corresponding drawing.
Frequently asked questions
Are all BMT40 tool holders interchangeable?
The BMT40 label alone does not establish interchangeability. Compare the turret interface, locating features, mounting-hole pitches, tool position and required clearance for the specific holder and machine.
What does A mean on a BMT holder drawing?
It depends on the drawing. In the BMT40-B25-H60 example, A is the 60 mm bore centre height. In the BMT40-C20-H55 example, A is the 30 mm lower-step height. Always retain the feature definition and unit.
Can the holder dimensions determine machining performance?
No. The listed dimensions identify geometry, not allowable loads, accuracy or tool life. Performance depends on the complete tool assembly and application; obtain the applicable limits and instructions from the tool manufacturer.