Use BevelWidth to specify how wide the inner or outer bevel should be. Do not confuse BevelWidth, which is the width of the bevels, with BorderWidth, which is the space between the bevels. 

If both the BevelInner and BevelOuter properties are bvNone, BevelWidth has no effect. To remove both bevels, set the BevelInner and BevelOuter properties to bvNone, rather than setting the BevelWidth to 0, as this involves less overhead when painting.

TBtnPanel Properties