Butt End with heavy-weight disc to keep balance of your rod including rubber cushion. WBP-2 has a 2mm-thickness balancer disc and WBP-5 has a 5mm one. 2mm disc (P2) has approximately 10g while 5mm (P5) has 25g. P2 and/or P5 can be easily added with mounting a F-20 Female Screw on your rod.