Guide to buying a cylinder A euro cylinder forms an integral part of many types of locks including multi-point locks used on PVCu doors and some mortice locks used on timber doors. Euro cylinders can be easily replaced and changing the cylinder is an easy way to 'change the locks'. Before you buy, you need to ensure you know what type, size and security of cylinder you require. Type There are three basic types of euro cylinder Single Cylinder - euro profile single cylinders offer key access from one side only Double Cylinder - euro profile double cylinders offer key access from both sides of the door Double Cylinder with Thumbturn - euro profile thumbturn cylinders offer key access from one side and a thumbturn from the other side of the door. Measuring Euro Profile Cylinders Euro Cylinders are measured in two halves from either side of the cylinder's 10mm centre section. For Thumbturn Cylinders, the first measurement is of the side with the thumbturn. Cylinders should be fitted so that they are flush with door furniture, particularly on the outside of the door.