This is the size most 540 or 550 electric motors use


Stainless Steel to Prevent Rusting.
Ultra High Grade Replacement Ball Bearing
1/8 x 3/8 x 5/32 ball bearing
High Quality inch size Ball Bearings, the inner diameter is 1/8", outer diameter is 3/8" and the width is 5/32", this is a popular size that could be used in many applications, each bearing has 2 metal shields to protect the bearing from dust or any possible contamination, also bearings are pre-lubricated with grease.
Item: Double Shielded Ball Bearings

1.125inch x 0.375inch x 5/32inch English Size
ID (inner diameter)/Bore= 1.125inch
OD (outer diameter)= 0.375inch
Width/Height/thickness= 0.156inch
Equal: R2-2Z & R2-ZZ
Size: 1/8" x 3/8" x 5/32"
Size: 0.1250" x 0.3750" x 0.1562"
Type: Deep groove ball bearings
Shields: 2 Metal Shields
Lubrication: Self Lubricated (Grease)
Quantity: two