I didn't know there were so many variations.
Mike has scratched the surface :yes4:. The Trend guide bushings we can get in the UK and EU come in a much wider range of sizes
which include both metric and Imperial sizes. The do sell a set of Imperial sizes
in the following sizes (Trend use the metric sizes
in their part numbers):
although other Imperial sizes are available (again metric equivalents in paranthesis):
That makes for a pretty wide range which can be further widened by the use of guide bush collars
used to make matching pockets and inlays. Trend also sell industrial quality sub-bases
to fit almost any router
The Trend guide bush design originated with the Elu MOF69 router in the early 1970s and carried on through the Elu MOF96 (in USA the 3303/3304) to the modern day deWalt DW613/DW614/DW615, Perles OF-808 and Trend T5 designs. Some other routers use them as well and deWalt in Europe also supply an adaptor to allow the DW624/DW625 to use this type of guide bush. Trend also sell as the "DE625T10" (not listed in the main catalogue, it is a spare part for the Trend T10 router). These adaptors are backwards compatible with the older Elu MOF177 (USA 3338/3339) and MOF131 models, although for some reason there is no compatibility with the DW621/DW622/DW626 (and Elu OF97/OF1) which saher the same likited range of cast metal guide bushes (in the EU 16, 20, 24 and 30mm). Trend are possibly unusual in having a very complete compatibility chart
on their web site which can be very useful.
Other European manufacturers have their own standards. For example Mafell use different guide bushes to everyone else, as do Festool (with what appears to be a unique system for each router in the range) whilst Bosch have standardised on the SDS bayonet mount type for the plunge routers. None offer anywhere near the range of sizes that Trend do
Note: Posted for completeness, especially for UK and EU members