"I had a need for a piece of kit like this and decided to go for the 300mm extension. I have to admit, I originally thought it was magnetic but soon discovered that it isn't. It does, however, hold the bit very securely using a different method. Experienced tradesmen will probably see it straight away but I found it after 10 minutes of fiddling around. It's strongly made and will stand a bit of pressure without bending. On the end of the bit holder is a knurled ring (the black bit) which is a 'collar'. Simply pull the collar back a few millimetres and pop in your chosen bit and release the collar. Job done!"
"can use an ordinary bit holder in the end if your actual bit is too short. Enabled me to reach underneath a 12" shelf without catching the power drill casing on the shelf & deflecting the angle, so exactly what I wanted."