Do all shoulder rests fit violins?

No, not all shoulder rests fit all violins. There are different sizes and styles of shoulder rests available, and the type that is best for a particular violin will depend on the size and shape of the instrument, as well as the player's personal preferences. Some shoulder rests are adjustable, so that they can be fitted to different violins, while others are designed for specific models or sizes of violins. It is important to choose a shoulder rest that fits the violin properly in order to ensure comfort and proper playing technique.