To determine the proper spring, you need to know the operating temperature and the grease weight. See the spring selection guide below.
For example, if the operating temperature of the bearing ranges from 60ºF to 80ºF, and you're using the grade 2 grease, then you will need a medium (silver) spring.
If mounting on an extension, use of an extra heavy (orange) spring may be required. The spring effectiveness will vary with application.
Spring Selection Guide