Nothing makes life easier than having a ‘master’ for the dimension(s) you have to measure. But a simple request for one with a dimension attached to it, for example, is not enough information to get something that will do what you want it to. Knowledgeable suppliers know that the term ‘master’ is generic in the broadest sense of the word and start asking so many questions it may seem that nothing is truly simple anymore. But it is in your best interests to answer those questions or you’ll end up with something that is more expensive than it needs to be or may not do what you want it to. The comments that follow will help you avoid these pitfalls.
What do you expect your master to do for you? The obvious answer is to provide a physical reference, but that’s not too enlightening. Is it being used to set a specific dimension for a measuring instrument? If the answer to this is yes, the next question that needs to be answered is: what kind of instrument? Often folks try to narrow things down by specifying they want a gage block to a special dimension so they get the most accurate master. The problem with this is the cost involved in providing a gage block to a special dimension, particularly when typical gage block tolerances are cited. And if the feature being measured is an outside diameter, a gage block may not be your best choice due to problems with instrument contact geometry. Some folks ask for a gage block and since they know it will be expensive, ask for it to be made from carbide or ceramics to increase its life. This will help where wear is a concern, but the increased cost of using these materials may not be worth it. Besides, temperature variations in use may negate the accuracy requested.