A US&S UB1 180 degree uni-directional crossing bell which will attach to my grade crossings. This one is good for residential areas since the sound can be emmitted in one direction. This is a mesh only, not the sound. You can change the bells out by clicking on the bell 0 or bell 1 in cmp and click the three dots and choose the bnsf crossing bell that you want. If there is not a front or rear bell in the effects list then there are no attachment points for that crossing, thus you cannot change the bell on those crossings.