A BMT boring tool holder must do two separate things: locate correctly on the turret and support the intended boring-bar configuration. A matching bar diameter answers only the second question, and even that requires checking the actual clamping arrangement. Select the holder from its complete drawing, then review the assembled bar position against the machining task.
The examples here concern two documented BMT40 boring-holder configurations. They help explain a common purchasing problem: two holders can have the same tool bore and mounting dimensions while placing that bore at different heights. Neither a shared family name nor a similar photograph settles the replacement decision.
Separate the tool bore from its position
The BMT40-B25-H60 holder records a 25 mm tool bore, identified as D, and a 60 mm bore centre height, identified as A. Its overall front-view height B is 83 mm. These dimensions describe different geometric features; the bore centre height is not the same as overall holder height.
Write each feature name next to the number when preparing an enquiry. A message containing only “25 bore, 60 height” leaves uncertainty about which height was measured and which drawing view was used. Include the original labels and units so that another person can follow the same measurement path.
The recorded bore diameter does not establish a suitable reducing sleeve, a clamping torque or the permitted boring-bar projection. Those details belong to the bar-and-holder assembly documentation. Do not order an assumed sleeve simply because the difference between two nominal diameters appears convenient.
Compare a height variant without changing the question
The BMT40-B25-H85 configuration also records a 25 mm tool bore, but its bore centre height is 85 mm and its overall front-view height is 108 mm. Both configurations list the following mounting dimensions in their respective records:
| Recorded mounting feature | Value |
|---|---|
| Locating-slot width C | 12 mm |
| Horizontal mounting-hole pitch E | 50 mm |
| Vertical mounting-hole pitch F | 60 mm |
| Mounting-face width G | 63 mm |
| Mounting-face length H | 94 mm |
This comparison identifies a positional difference rather than proving interchangeability. Check how the bore centre sits relative to the turret reference and the required cutting position. A change in height affects the configuration review even where the visible mounting fields match.
Build the enquiry around the complete bar assembly
Identify the boring bar separately from the holder. Record the bar designation, diameter and intended projection, then describe the cutting head or insert arrangement if known. Explain whether the operation concerns a through feature, a blind feature or a profile with a clearance restriction. A part drawing provides more useful context than the statement that the job is simply boring.
Show the intended gripping region and any features that must remain outside the clamp. If the listing does not establish that a particular bar can be clamped safely, obtain the relevant assembly instructions before installation. Dimensional similarity does not supply missing clamping information.
Keep coolant requirements as a separate enquiry item. A photograph of a hole or fitting cannot establish the internal coolant route, connection type or pressure limit. State what the machine and boring bar require and request confirmation of the selected holder's documented provisions.
Review space before choosing extra projection
A holder drawing and a bar drawing should be reviewed together with the intended machine setup. Consider the chuck, workpiece, adjacent tools and the path used to enter or withdraw from the feature. The listing does not provide a universal clearance allowance for these conditions.
Do not treat a longer available projection as automatically useful. First identify the reach demanded by the part and the space occupied by the complete assembly. Any allowable extension or load limit must come from applicable tooling documentation; it cannot be calculated from the holder's outside dimensions alone.
Request one clearly identified configuration
Send a marked-up turret-interface drawing, the complete holder designation, the bar details and the required tool position. Specify quantity and identify any sleeve or accessory being requested. Ask the quotation to distinguish the holder itself from additional items rather than assuming that a family photograph represents an included package.
The tool holders and adapters catalogue can help locate a candidate, but the final comparison remains configuration-specific. Retain the drawing references with the enquiry so that a later change to bore size or centre height does not silently become a different product. Installation and cutting limits should be checked independently of the commercial quotation.
Frequently asked questions
Does a matching boring-bar diameter prove the holder fits?
No. The turret mounting, bore position and actual bar clamping arrangement must also match the intended assembly.
How do the two BMT40 examples differ?
Both list a 25 mm tool bore. Their recorded bore centre heights are 60 mm and 85 mm, respectively; that difference must be checked against the setup.
Are sleeves and accessories included?
The dimensions do not establish an accessory package. Identify any requested sleeve or other item separately in the quotation.