The Zaret Shoulder Rest, a simple but effective solution for students' shoulder rest woes, comes in three sizes:

Extra-Small: 10.5cm long, 5cm wide, 1.75cm - 3cm high (for 1/16-1/8 size)

Small: 13.5cm long, 5.5cm wide, 2.2cm - 4.5cm high (for 1/4-1/2 size)

Large: 16.5cm long, 5.75cm wide, 2.5cm - 5cm high (for 3/4-4/4 size)