Listen carefully and I will tell you how to do it.
Get the standard plastic screw end (from gardiners - to fit the plastic adjustable gooseneck). It goes inside the end of the pole. Take the length wich will be the end of your pole.
Estimate where it will be wide enough for the screw to fit in and cut it at that point. Take the top bit. Turn it upside down (so the thin end is pointing down) and glue the screw thread into this.
Take the other peice of the section you cut in two. this will be the end section of you pole. The piece you have with the screw glued into, should slide into this ( so the screw is at the top). Glue it in place.
Tada. You now have a top pole section that is dpouble thickness around the screw thread for strength! although you cannot tell from the outside.
To make it treble thickness, the bit with the screw thread which goes inside the otther bit is probably quite long, cut an inch or so off the other end to the screw. Cut this into two - lengthways - before you glue that section into the other.
When you have achieved the double thickness bit above, take these two pieces cut lengthways and glue them on the outside of the top pole sectiond around the screww neck. This in effect makes it treble thickness and very strong.