These Bosch 30/40 amp 5-pin relays are a staple of the automotive industry. They are useful for a number of wiring configurations included polarity reversing circuits.
Load pin (87) is rated for 40 amps; alternative load pin (87a) is rated for 30 amps.
This product can expose you to chemicals including lead, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, go to www.p65warnings.ca.gov.