Tonearm Geometry and Terms

Best Tractor is just a tool and it is prepared in accordance with the Tonearm Geometry as defined by the manufacturers.

What are these parameters?

1. Effective Length

Please read the link below:

What an excellent picture which tells everything!

In practice you may measure the Effective Length of a tonearm by a common ruler:


This method is not accurate but it will give some insights into the designer's intention in case the Tonearm's specification is not published.  


When your tonearm headshell has a slot for mounting cartridges, then the Effective Length becomes adjustable. This is a pre-requisite for using the Best Tractor.

The right headshell comes with a slot which allows for Effective Length adjustment. In contrast the left one has fixed bore holes.


Not all tonearms allow Effective Length adjustment. SME tonearm is one example.

Can I order a Best Tractor for SME tonearms?

The answer is Yes.

But we need your input on the Mounting Hole to Stylus Tip [MHST] distance of your cartridge. And the Best Tractor becomes Turntable/Tonearm/Cartridge specific. This means any change in one of the three (3) components the Best Tractor may not be applicable.

Please read the following link for more information regarding SME toenarms:

2. Mounting Distance

It is the same as the "Pivot to Spindle" Distance as explained in this link:

For a certain turntables which are partnered with a particular tonearm this Mounting Distance is fixed. Example is Rega Turntable with Rega Tonearms, Origin Live Turntable with Origin Live tonearms, Technics SL1200 turntable with stock arm, etc.

But some turntables do have armboards which are Mounting Distance adjustable. Examples are Galibier, TW Acustic Raven, Clearaudio. Some tonearms are Mounting Distance adjustable, the most famous is SME tonearms.

Please note that Mounting Distance is a CRITICAL parameter for perfect alignment and hence we sometimes ask our users to confirm the distance with us before we prepare a Best Tractor for their requirement.

3. Overhang

This is very simple:

Overhang = Effective Length - Mounting Distance

4. Offset Angle

To get the best result, headshell is bent toward the spindle centre. The angle of the headshell in relation to the armtube is known as the Offset angle.

An example from the Micro Seiki 237 tonearm. The headshell slot for mounting the cartridge forms an angle of 21 degree to the armtube:  

5. What we need from you

We do not have data on all tonearms and often we depend on user inputs. Please help us by reading the tonearm manual and quote us the Effective Length and Mounting Distance. It will help a great deal if you take up a common millimeter ruler and take a ball-park measurement to confirm what is said on paper.

6. Other Parameters

Please read the following link for Azimuth, VTA and VTF settings:

Tips on Getting Perfect Alignment


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