Spark Arrestor AdapterWill need this adapter along with a Spark arrestor Click Here! We developed an internal adaptor for the trials bikes that don't have a silencer end you can attach our spark arrestor to, the internal adapter uses 3 set screws to secure. Then our standard spark arrestor (31. 5mm) attaches to the adapter with 3 set screws. Internal Adapter is for trials bikes that do not have a silencer end that extends out for a spark arrestor to attach to On the