Switch size depends on what you are using to activate the switch - sometimes you want to use a finger or other small area... Here are the options (please add to) - there are other suppliers available, where no supplier noted, a simple web search will find you one:

The ‘conventional’ solution in the UK - this is a great little switch that comes with a flexible strap and this allows you to strap it around lots of things - including fingers. Strapping it around a finger can be a bit cumbersome though (since the switch is relatively big compared to a finger). Lots of suppliers of this, made by AbleNet (US).

• Diameter: 36mm
• Mounting: Base and/or strap (and a handy screwdriver that you’ll end up with a million of)

This is a handy switch for squeezing between fingers, or it can be mounted on a flat surface or something like a leg. The little raised bit at the end can be useful (to locate the switch) but also you need to be specific about where you press it. Adjustable pressure can be useful.

• Diameter: 50*35mm
• Mounting: None really - velcro or stick it

A super light touch switch, but a bit cumbersome to mount on something that isn’t a flat surface or wide diameter (e.g. leg, head etc). Have to be fairly specific about where you press it and so locating it accurately can be a pain. Slightly taller than it is wide, so not amazingly stable.

• Diameter: 45*13mm
• Mounting: None really - velcro or stick it

There are a number of keyboard switches you can get that are nice and small and with OK activation pressures. Check out the category in RS (click this link) and also the millions of other switches in RS.

These could be mounted on a velcro strap, moulded into silicon or an orthosis. I’ll post some case studies of this on this page eventually.

• Putney hospital Small Plate Switch
  • £35 - Compass EAT service - 0208 7804500

• Adjustable Pressure Pinch switch
  • Diameter: 18mm
  • Mounting: None?

• Mini Cup Switch
  • Diameter: 45mm
  • Mounting: ??

• Trigger Switch
  • Diameter: 23mm
  • Mounting: sticky pad