These are usually produced IMPERIAL sizes and in the case of the Cutters they are the most common cutters used with the majority guiding the cut with the aid of a bearing.

With regards to Imperial Template guides these are produced in a variety of sizes with the largest diameter 1" 0r smaller. This will restrict what cutters can be used. How many router users here in Australia use Imperial cutters and Guides.

To assist when using imperial I sent a DVD to Carb-I-Tool to be included with their set of guides, also requesting that they produce larger diameter guide for use. This DVD is an introduction to the use of the template guides {Imperial]

Why is there a need for the Larger Guide ????
1. as stated above a larger range of cutters can be used. 2, The cutter is visible during the process, 3, The cutter has less chance of over heating as the swarf will disperse more readily, 4, The chuck of the router will penetrate through the 40mm / 1-1/2" guides to give you extra depth of cut.

Metric Cutters and Guides are easier to work with when working out the "OFFSET" when doing your calculations. It has been quoted that 90% of all routing can be achieved using the router in the table mode. This will depend on what you wish to do with your router. Over the past 30 years I have found that I can do 90% of my routing in the plunge mode with the aid of the guides projects that are impossible to do in the table mode. I must also add that there are routing processes that should be done in the Table Mode. I have since produced a simple Jig where some of those processes can be achieved with greater safety awareness. Fingers can not get any closer than 80mm to the cutter. A method that I have been teaching with success at our local Mens shed

Get More from your router by Tom O'Donnell: Crafts & Hobbies | Blurb Books Australia This will lead you to a book converting the metric to IMPERIAL [scroll down See More books and Magazines}