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You are correct, spline is different than torx.Although you can use torx drivers or bits, you can ruin the screws if you are not careful.Been there, done that.
Torx have points, whereas spline are flat on top of there grooves like you said similar to a driveline in a car.
Also years ago, they were also called bristol keys.
You can find them at
www.mcmaster-carrsupplycompany.com which is listed in the Bladeforums links section under related sources.
I bought mine from them, as I have both Microtechs, and Masters of Defense(MOD) knives with spline screws.
I got 1 set of L-keys, small packet marked bristol keys, and 1 set of a wrench, and insert bits.Both sets were under $10 each, and they have no minimum.
They have 3 outlets in the country.1 in the southeast, 1 in the northeast, and 1 in Los Angeles,Calif.
When you are removing the screws, make sure you heat the screw with a hair dryer, or some sort of heat gun, as they use loc-tite to keep the screws from getting loose.
Hope this helps.
Larry