A:
There are two ways of going about this. The first requires you to measure your rod tip using a "rod tip sizer." Just like a drill bit sizer, a tip sizer requires you to stick the broken tip into holes of varying size until you find the best fit (the tightest hole that the tip will fit into). The hole will have a measurement next to it, usually in both 64th's of an inch and millimeters, so that you can order the correct size. Unfortunately, we don't have a tip sizer available, but you could easily find one through a Google search.
Your second option is to buy a rod tip repair kit. These kits contain multiple tips so that you can try different sizes and use the best fitting one. These kits also include the glue to attach the tip to your rod.