Yellow Medium Universal/Acme Thread Boat Hook Three Sided Bristle Brush by Sea DogÂ®. Injection Molded Nylon. These three-sided bristle brushes fit all Sea-DogÂ® boat hooks and all universal threaded devices. Available in soft, medium, and stiff bristles. Soft bristles are safe for gelcoat, paint and plastic windows. The medium bristle is a good overall brush for textured and non-skid surfaces. Stiff bristles are effective for jobs below the waterline, teak and other tough cleaning jobs. Side bristles make it easy to clean in hard to reach places. 10-1/2" head is longer than industry standard covering a larger cleaning area.