Proxxon Brass Brushes, Cups & Wheels Proxxon Brass brushes - No 28961 Ideal for working on alloys, copper, precious metals, semi-precious stones, plastic and wood. Acid proof. Electrically neutral, thus suitable for working with electronic components. No 28961 size 8 pack of 2 Proxxon Brass Cup brushes - No 28963 Ideal for working on alloys, copper, precious metals, semi-precious stones, plastic and wood. Acid proof. Electrically neutral, thus suitable for working with electronic components. No 28963 size 13 pack of 2 Proxxon Brass wheels - No 28962 Ideal for working on alloys, copper, precious metals, semi-precious stones, plastic and wood. Acid proof. Electrically neutral, thus suitable for working with electronic components. No 28962 pack of 5