40mm plastic drainpipe is the right diameter to take most of the shafts or handles of my tools. a 2m length is cheap too. After measuring the shortest tools in my kit (a stanley knife and permanent marker) I cut the drainpipe into 13cm lengths. This is long enough so tools are properly held upright, but not so long you can't get the short tools out.
The toolbag, being a bag and all, is too floppy to hold the tubes neatly upright, so i cut a baseboard out of 6mm ply to hold them on. As I also have other tools such as a spanner roll and cans of WD-40 and degreaser to keep in the bag I used more 6mm ply to make partitions. One long one for the spanner roll and long tools and a smaller one to store cans, bottles and tape.
The corners are chamfered so the baseboard fits into the bottom of the bag easily and to avoid damage to the bag (or me) from the sharp corners.
This photo shows the baseboard and partitions. The partitions are held in place with triangles of 40x40 wood, screwed into through the ply. The tubes are epoxied into place with copious amounts of araldite on the base of the tubes and along the lines of contact between other tubes and the wood. They're pretty sturdy, but may need reinforcing over time.
Here's the bag with the board in it. You can see the partitions and tubes in place.