I personally would not put any of the ER extensions into a hand router as their shanks are just too long. Going by the Techniks guidelines, a collet extension should not extend more than 4x the shank diameter. So in your case, it could not extend more than 32mm, and that would be measured from the face of your routers collet all the way to the face of the collet on the extension. You would have to find a VERY SHORT extension for this to work. I would say a 50mm shank length max, hoping that you could get more than 35mm of that shank into your routers collet in order to get the maximum recommended extension.