The AT-850 mixing tip is designed for use with Weld Mount adhesives packaged in "non-cross contamination" cartridges — the cartridges with the gray caps.
The AT-850 tip has a unique design which prevents cross-contamination of the adhesive cartridge orifices when the mixing tip is removed between uses - so the cartridge tip doesn't get plugged with cured adhesive by accident.
Both the AT-850 mixing tip and the cartridges it is used on have nozzles which keep the two components of the adhesive completely separated until they are actually inside the mixing barrel.
Note — Once you start using (gunning) the adhesive, the mixed product inside the tip will set in about 4 minutes if not used.
For jobs with long periods of time between applying the adhesive, you will either have to replace the tip, or after 4 minutes have passed gun the adhesive in the tip onto a piece of cardboard, replacing it with new adhesive to gain an additional 4 minutes of time - thus saving a mixing tip. (You can feel the difference in resistance when you have expelled the thickened adhesive.)
By either method you sacrifice an amount of adhesive equivalent to the volume of the mixing tip, so try to plan your project so the work keeps moving along.
Compared to traditional 6" mixing tips used by other manufacturers, the 3-1/2" AT-850 will save some expense in lost materials. The AT-850 tip has internal baffles and square corners - both create the swirling effect that thoroughly mixes the two adhesive components. Experimentation by Weld mount engineers has resulted in the shortest possible length that would get the job done.