STD 628 ZZ Skate Rated "Standard" Bearings 8mm Set of 16

Set of 16 STD 628 ZZ skate rated "STANDARD" 8mm bearings with two steel seals and cage, balls, outer ring, and inner steel ring for 8mm axle diameter.  These skate rated STANDARD are special bearings for figure skating. The "Skates Rated" calibration is based on a specific mechanical adjustment designed to withstand the forces involved in skating.
 
Radial Clearance: This takes into account the space between the balls and the raceways of the rings. In the Skate Rate calibration, an intentional clearance is left. This prevents the bearing from seizing up when a little dirt gets inside or when heat expands the metals during intense training.
Lateral Load Capacity: The bearing raceways have deeper grooves to prevent the balls from slipping off their axles or "biting" the metal when subjected to lateral pressure.
 
Groove Depth Calibration: A bearing calibrated for skating has deeper ball grooves to increase structural stability under impacts (jumps, spins).
Maintenance: Metal-shielded (ZZ) bearings are generally non-serviceable or harder to clean without popping shields out; they are designed for clean indoor rink environments or light outdoor recreational use. 
Shield Type: Dual metal shields (ZZ), which reduce friction better than rubber seals (RS) but offer less defense against fine liquid or heavy dirt immersion. 
Size Constraint: Unlike the highly common 608 skate bearings (which have a 22mm outer diameter), 628 bearings have a larger 24mm outer diameter. They will only fit specialty quad skate wheels or artistic inline plates explicitly machined to accept 24mm variants.

STD Bearings Use Summary
Beginner: Balanced calibration between speed and impact resistance = STANDARD
Precision: Calibration with finer tolerances for maximum inertia (rolls longer without pushing off) = DEEP GROOVE
Competition: Calibration focused on minimal friction, with mirror-polished balls and ceramic coating = CERAMIC