# What's the difference between an A mandrel and a B mandrel?



## navycop (Aug 23, 2011)

I see some websites offer 2 different types of pen kits. They say one fits an "A" mandrel and one fits a "B" mandrel.


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## Grampy122 (Aug 23, 2011)

*From the Bear Tooth Web site*

Are your bushings compatible with my mandrels? 
The “A” series of bushings are designed to work with the standard “7mm” mandrel systems. However, they are only guaranteed to work with the mandrels sold by Bear Tooth Woods. They likely will work with mandrels from other suppliers, but no guarantee is given. The “B” series of bushings are designed to work with the larger “B” mandrel system that is only made by Berea Hardwoods, they will not work on any other mandrel system. This larger system has some significant benefits and is well worth the added cost.

Why are there two sizes of mandrels? 
Berea Hardwoods and Bear Tooth Woods support two different sized mandrel systems. The “A” sized system is mainly used for the pens based on the 7mm tube (with two notable additions, the cigar pen and the sierra pen), while the “B” sized system is used with all other kits.

The “B” sized system has the benefit of being thicker than the “A” system. This added thickness provides a much more stable platform for making pens. This stability reduces the out of round problems that can occur when making pens.


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## PenMan1 (Aug 23, 2011)

The short version.
All "a" mandrels are 7 mm in diameter. All "a" bushings will work with that mandrel.
All "b" mandrels are 8 mm in diameter. All "b" bushings will work with that mandrel.

The reason for different sizes is that some bushings sets (cambridge, for one)are to heavy for 7mm mandrels and would cause "mandrel whip" on a 7 mm mandrel.

Any "a" bushings that don't fit "a" mandrels or "b" that don't fit are DEFECTIVE as both a and b are industry standards that have exact written size specs.


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## PenMan1 (Aug 23, 2011)

To my knowledge, (I have built at least one of every set I can find), only 4 sets use "b" bushings. Cambridge, Perfect Fit, Cigar and one other.

The others that CAN use "b" bushings (including cigar) are also available in "a" sizes.

My recommendation would be to buy an "a" mandrel. If you move to the sets I listed, you can buy TBC equipment for those bushings for less than a "b" mandrel.

Respectfully submitted.


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## navycop (Aug 24, 2011)

Thanks. I have two mandrels. One  I got from PSI. It is just the rod with a nut on the end. I chuck it in my jacobs chuck. The 2nd is from Woodcraft. It is the one  that fits on a shopsmith with the set screw. I never paid attention to if they were A or B. I only have a few bushings for now. I wanted to make sure to get the right ones in the future.


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## BigShed (Aug 24, 2011)

PenMan1 said:


> The short version.
> All "a" mandrels are 7 mm in diameter. All "a" bushings will work with that mandrel.
> All "b" mandrels are 8 mm in diameter. All "b" bushings will work with that mandrel.
> 
> ...



Not quite my understanding.

All "A" mandrels are 1/4" in diameter

All "B" mandrels are 5/16" in diameter.

If an A mandrel was 7mm in diameter it wouldn't fit through a 7mm (OD) tube, which is 6.35mm or 1/4" ID.

I used to make my A and B mandrels from 1/4" and 5/16" silver steel or drill rod.

I say used to, as I have completely changed over to TBC bushes since I purchased my metal lathe.


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