Saunders Broadhead O-Rings are a must have for any serious bowhunter.
The absolute best way to broadhead tune your arrows is to ensure all of your broadheads face in the same direction (for example, aligning a 2 blade broadheads so that one of the blades is always in-line with the cock feather).
By installing an O-Ring on your broadhead threads, it can change the direction your broadhead faces as the end of position of the thread installed in your insert will change. It is a bit of trial and error, but you can use one or more O-Ring to get your broadhead arrows consistent this way.
O-Rings will also hold your tip secure in the insert so that they don't rattle loose after shooting, which is also a real treat for target shooters.
100 O-Rings per pack. These can perish over time so it is best to have spares on hand.