Types of Tool Holder Taper Shanks
Cat Tool Holders have a slot that goes through both sections on the flange. This flange design is the main difference between CAT & BT Shanks. Their size is most easily determined by measuring D1 or D2 and look significantly different when compared. CAT is considered the US Standard for tapered shank tool holders.
BT Tool Holders have a slot that goes through the top (usually) larger flange and partially through the bottom. This flange design is the main difference between CAT & BT Shanks. Their size is most easily determined by measuring D1 or D2 and look significantly different when compared.
NMTB Tool Holders have only one flange and may either be large resembling BT or small resembling CAT. They do not taper all the way to the pull stud, which is the easiest way to differentiate NMTB. The easiest way to determine size is by measuring D1 or D5. NMTB may also be referred to as Quick Change Shank.
HSK-A Tool Holders do not much resemble that of the others. It is of German design and doesn't use a retention knob, rather a dual contact method providing more rigidity. Determining HSK-A size is very simple, as the D2 measurement in mm (millimetres) is equal to the size #.
Tool Holding Types
Solid End Mill
End mill holders have one solid inner diameter that does not taper and always have 1 or more set screws that hold the tooling rigid. These are readily available and economical for milling.
Their inner diameter size can be measured by calipers and is often labeled on the flange. Projection is measured from the bottom of the flange to the very end of the holder.
Collet chuck holders hold various types of collets, the most common being TG, ER, & DA. They come with a collet nut that can either be hex or slotted which is threaded on & off to hold the collets that hold the tooling.
The size and style collet that they hold can be measured using charts. Projection is measured from the bottom of the flange to the end of the collet nut when it is loosely tightened.
As the name implies, the inner diameter in these tool holders is tapered. There are no set screws and the tooling is fit by a male / female component. There will always be a slot in the taper shank seen in the two pictures above.
To find what size MT (Morse Taper) you have, measure the largest point of the inner diameter and compare to the "Large End" on the chart seen above. Projection is measured from the bottom of the flange to the end of the holder.
Face / Shell Mill
Face / shell mill holders will have a male pilot and key width that a mill will fit into. A set screw should be present in the pilot and will hold the mill in place.
Both pilot and key width can be measured by calipers and correspond to the face / shell mill size. Projection is measured from the bottom of the flange to the end of the pilot.
Shrink Fit holders will have a solid inner diameter similar to other milling holders, but do not have set screws. They are slimmer and have excellent gripping force. They are heated when changing tools, expanding the diameter and cooled to provide an interference fit.
Their size is measured by calipers similar to solid end mill holders. Projection is measured from the bottom of the flange to the very end of the holder.
Hydraulic Holders / Chucks
Hydraulic chucks will have set screws much closer to the flange and will have a solid inner diameter similar to end mill holders. They use oil to generate pressure and deform the holder’s ID around the tool shank and provide excellent gripping force.
Size is measured with calipers and projection is measured from the bottom of the flange to the very end of the holder.
Tension Compression Tapping