Cages look different between makers because of production standards, equipment, and raw materials. Appearance is only surface; strength issues hide inside. Point by point. First, poor appearance traces to weak welding. Poor fusion means weak strength; a missed weld is a fatal defect that can cause real trouble — even injury and loss — in normal use. Second, a stiff half-side door comes from uneven pitch of the spring-type spiral wire joining upper and lower mesh. On a standard cage, spiral-wire pitch should be 50 mm. Xintongnuo runs these on high-precision coil-spring machines for a constant 50 mm pitch, so the half-side door opens and closes smoothly. Small shops on ordinary equipment land above or below 50 mm, and the door seals poorly and feels rough. Third, standard cages use 6.0 mm wire. Measuring 5.9 mm is a big downward tolerance that hits load directly. Bring calipers: measure the wire and the channel thickness, and you can judge whether the cage reaches its rated load.