This is a modern variant of a classic armrest design; the top is a flat bar with a slightly rounded-off corners. This item is often used for vintage restoration work.
The armrest is fixed on by each of the 2 legs being attached to a tension hook with a fitting quite like an old-fashioned hexagonal bracket shoe. The fittings are included with every armrest. The armrest will then sit reasonably comfortably level with the top of the tension ring - or a little higher, if preferred, depending on the exact configuration of the tension ring & brackets.
This armrest is designed for 11"- 12" diameter banjos and it's relatively easy to carefully bend it to fit your banjo (the legs are twisted at an angle to the top and, being made from brass, can be carefully bent). We quote the radius as 5 ½" - 6" but it will go a little more than that at a push.
The dimensions (all approximate) of the armrest are:
150mm long x 10mm wide x 3mm deep; the "legs" are approx 42mm long and have fixing holes about 38mm from the top.
If you need to work to precise measurements for a particular banjo, please e-mail your requirements - we can sometimes alter an armrest to give different clearances from those given above.