An assembly for forming an injection device, comprising: a foot to be placed on a skin; a body comprising at least one needle, the body being movably mounted to the foot for allowing movement of the needle towards the skin, the needle extending out of a second contact surface by a predefined distance for limiting a penetration depth of the needle; first friction means for preventing movement of the body relative to the foot for causing a sudden acceleration; the assembly further comprising second friction means for creating a dynamic friction when the needle is moving towards the skin for keeping the skin stretched.