The photo below shows location, size, and part number for the Posi-drive screws securing the outer gearbox cover of a 1969 Triumph T120R.
If you use Phillips screwdrivers on the large screws holding on your Triumph's three covers, you may have noticed how hard it is to get a screwdriver that fits exactly right. That's because the screws are Posi-drive, not Phillips. If you look closely you'll see that the Posi-drive has eight ridges and not four.
It's important to use a Posi-drive screwdriver because Phillips screwdrivers don't engage properly and they damage the screws, rounding them off inside. A Posi-drive bit is waaay more secure in the head, and you don't even need to turn blue in the face exerting so much inward pressure as with a Phillips.
If you truly love your motorcycle, get some Posi-drive screwdrivers and use them with pride on your Triumph's gearbox, primary chaincase, and timing covers. They are a very modest investment, and once you use them you'll look back and wonder how you could have been so barbaric as to use Phillips screwdrivers on Posi-drive fasteners. Forgive them Father, for they knew not what they did.