Some rifles like the HFT-500 have a cheek piece that can move up and down. The advantage of this is the ability to get the perfect fit for your cheek on the stock no matter how high or low the scope is set. Some shooters use scopes with a 56mm objective (front) lens and some use scopes with a 32mm. This means that on some rifles you will have to use a high mount and some, you can use a low. The adjustable cheek piece allows you to always have your eye perfectly centred on the scope, no matter how big or small the scope is.