I am listing 30 S-sized Tai-Raba (鯛ラバ) caps for sale. These are equivalent to the S size of Jackall's Bin-Bin Backfire Cap. They feel slightly larger than Jackall's, perhaps. To make them M size, you will need to drill them with a 2.9mm drill bit. (Please note that any modifications are at your own risk.) The size is based on my personal subjective experience using them. When considering a purchase, please check the size in the 3rd image before buying. No price reductions will be made. There may be manufacturing burrs, so please remove them before use.