dp_prop_sphere
dp_prop_sphere is an e0 available in all 
Source games. It is identical to prop_physics, however it has a preprogrammed spherical collision box.
Entity Description
This entity is a duplicate and functions the same as a prop_physics. The only difference with the db_prop_sphere is it uses a coded collision model, a perfectly round sphere (and is cheaper then a regular prop_physics). Use this entity with models such as marbles, rocks, buolders, etc. It will roll perfectly with no rockiness (that you'd usually get with a prop_physics). It has no use as a standard prop physics, only use for something round shaped that you want to roll smooth & perfectly.
- This entity uses all the same functions as prop_physics. See that entity for a list of it's properties you can use.
You don't need to edit any properties in this entity. Just place it and use it like you would with a prop_physics, only difference it'll use the perfectly round sphere as a collision.