The Pin Diameter is probably the easiest one, as it is exactly how the name suggests. Simply take out the bucket pins and either measure the width of the pin, or the size of the hole in the boss fitted to the hanger! These will usually be between 1 and 1.4 inch for the Micro Excavators and Mini Excavators.
The Pin Centres is another easy one, however it can also be quite misleading if you measure from the wrong points. The pin centres is only massively critial if you have a pin grab / quick coupler, as this can be the difference between the latch locking on to the bucket or not. If you do not have a pin grab or quick couple fitted, then this measurement is not too important, however closer to the standard measurement the better, as this is what your excavator is designed to work with.
Between the Hangers.
The Dipper Gap is one that can often get confusing as there are also other common terms for the measurement, for example ear gap, hanger gap, dipper width, and bracket width to name a few. This measurement is quite critical, however there are usually /- 0.08 of an inch.
You can measure this either by using a ruler or tape measure on the inside of the hangers, or you can also measure the width of the bucket link / H link, however please lookout for any wear and tear on these components, as it may effect these dimensions slightly!