Hot Tub control system circuit board fuse.
Product Notes: Used on many Balboa & other systems. Keep a spare fuse on hand.
Amperage: 300mA (0.3A)
Type: Time Delay (Slow Blow)
Dimensions: ¼" x 1¼"
Max Voltage: 250VAC
Reference: Balboa 21581, 35-0027-K5, 389319, 48K9778, MDL-3/10-L