"What could go wrong with replacing a like for like euro cylinder? Took less than 10 mins to change and works well. However, to get the RIGHT cylinder took me three attempts and a visit to a local professional locksmith company. Apparently the cylinders could be measured in one of three ways, depending on the supply company. There is nothing in the screwfix catalogue, or on the web site, telling the uninitiated what their sizes mean. A simple diagram showing how the 35/35 is arrived at would solve this. Took me over a week to get the right one and 10 mins to fit."