I have made several rod extensions using old, or scrap rod handles. Just cut to size and either up-sleeve or down-sleeve to fit existing rod.
If you need a threaded extension and have an old rod with a rubber button fitted the rubber button threaded part is likely to be a 3/8"bsf thread, which was the fishing tackle standard (still quite common and standard with Shakespeare). Cut off a piece of the old rod handle and screw in a bolt and then cut off the bolt head. The new handle can then be sanded to suit and becomes a 'screw in' extension. 3/8"bsf is also the coarse fishing standard for most things, and threaded parts, that can be modified, are readily available on ebay.
