What is the difference between a 'Type 30' and a 'Type 20' brake chamber, and why does this matter for brake adjustment limits?

1. Type 30 has a larger surface area (30 square inches), which means it has a longer maximum legal pushrod stroke limit (2 inches or 50 mm) than a Type 20 chamber
2. Type 30 is used only on steering axles and Type 20 on drive axles
3. Type 30 chambers are hydraulic and Type 20 are pneumatic
4. Type 30 operates at 300 psi and Type 20 operates at 200 psi