To start with, place the two Swing Arms parallel and about 6 inches apart. Once you get more proficient at this drill, you should move the Swing Arms a bit closer together, so that there is not much room between your putter and the Swing Arms.
If you are a linear putter, and tend to take the club straight back and through using a face-balanced putter, rotate the Bristles so that they are pointing upwards (see photo above) Conversely, if you use a heel-toe balanced putter and tend to swing slightly inside-toinside, rotate the Bristles so they are horizontal, or nearly touching the floor (see PDF below).
Now, simply practice your stroke by swinging between the Swing Arms, ensuring you avoid hitting them either on the back swing or the through swing. Move the Swing Arms closer together as you become more proficient at this drill. When the Swing Arms are close, and you’re still not hitting them, you know your putting stroke is good.
For the more advanced players you can repeat the above drills using just one hand only; this is a favourite drill of many pros and leads to fantastic control.
