The cheapest gas spring, the outer tube is 1.0mm, the inner tube is 1.5mm, the inner part is basically made of plastic parts, and the sealing ring with poor airtightness is used. It can't pass the BIFMA test. The lifting comfort is poor, and it will shake. When people stand up, there will be a noticeable impact sound, and there will be a noticeable sinking feeling when sitting down.
Outer tube 1.2mm (or 1.0mm), inner tube 2.0mm, with plastic parts and steel ball bearings. A better brand of the secondary gas spring may pass the BIFMA test, but because the 1.2mm outer tube is not guaranteed to pass the pushback test, it can only be said to be a side ball. Its performance in all aspects is better than level 1, because it has a good price-performance ratio, many domestic products use this standard gas spring.
Outer tube 1.5mm, inner tube 2.0mm, all plastic parts use steel ball bearings. The three-stage gas rod can really pass the BIFMA test. The brand's corporate products are basically matched with this grade of the gas spring.
The outer tube is 1.5mm, the inner tube is 2.0mm, the inner tube is black and has been quenched and hardened. It is not very commonly used. Some high-end brands will make products that exceed the BIFMA standard and specify special specifications: the above four are conventional, but some brands will make special orders due to product positioning or other reasons.
Note: All Sihoo ergonomic chairs use gas spring above class 3 (including class 3)