NONE whatsoever, they are exactly the same same part when it comes to ordering. People and industry has different names for them. Here are some other variations.
Door lock ( often confused with the actual lock that a cylinder barrel turns.)
Yes, You can order extra keys at the checkout page.
To measure your cylinder follow this link to the guide its will sow you how to remove your cylinder barrel and how to measure it Click here for more details.
You will get three precut keys, More are available at time of order. You cannot add more once the item has been dispatched.
Thumbturns are ideal if you want to be able to use a cylinder from inside without a key. cupboards etc or houses where you have a dog that is constantly coming and going outside
Feel free to contact us if you need anymore information.