For some time I have noticed that some drill chucks had tapers specified a "B" numbers i.e. B10, B12....... instead of the more usual JT (Jacobs Taper). I was interested to discover the spec. of these tapers, and did far amount of Googling without success. Some time later I visited the Jacobs site for interest and came across the information somewhat hidden on their site - not the first place to look for details of a "rival" taper.
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At the bottom of the page is "Technical Information: Download.pdf"For general interest the Din B tapers are base on part of a Morse taper. e.g.. B10 & B12 are based on the small & large ends respectively. Hope the reference will be of some help/interest
Regards Brian