The t slot aluminum extrusions can be with 4mm T-slot, 6mm T-slot, 8mm T-slot, 10mm T-slot, and so on. There’re mainly two reasons for this difference.
It is harmonious for a small cross-section has a small slot and a big cross-section has a big slot. For instance, the 2020 aluminum profile is with a 6mm slot, and the 4040 aluminum profile is with an 8mm slot. (There will be extra 0.2mm for real slot size for installing bolts and nuts.)
Considering the light and heavy load structure, the aluminum profile with a small slot is suitable for light frame structure; the aluminum profile with a large slot is used for frame structure with high-stress intensity. For large-section aluminum profiles, the slot needs to be larger, so that aluminum profile accessories that meet the load-bearing requirements can be installed. If the slot of the aluminum profile with a large cross-section is smaller, the specifications of the aluminum profile fittings installed will be smaller, and the aluminum profile fittings cannot bear the type of aluminum profile, resulting in fracture, which affects the later use. However, if the aluminum profile with a small cross-section is equipped with a large slot, whether it is price or load-bearing, it will cause a waste of aluminum profile accessories. The 20 series(2020) of the aluminum profile is with 6mm T-slot. Most of the 30 series(3030) are with 8mm T-slot, there are also 6mm T-slot. Most of the 45 series(4545) and 50 series(5050) industrial aluminum profiles have a slot width of 10mm, with M10 bolts, and a small part of the slot width is 8mm. The aluminum profiles above 5050 are mostly 8mm double slots, and there are also 10mm and 12mm single slot aluminum profiles. The wider the slot, the larger the bolts and nuts, the greater the strength. The 9090, 100100 large aluminum profiles are with double-slot 10mm. There are also some special-shaped aluminum profiles with special slot sizes, such as 5.5mm, 5.2mm, 4.5mm, 6.5mm, 7.5mm, etc. These T-slot aluminum profiles will be assembled with special bolts and nuts.