Hi MWM
Depending on the age of your router, Sears has always had a special unique guide bushing set, that you attached to the 3 small holes around the router bit center opening.
The steel guide bushing came in a set of 3, if I recall, and are the same guides used with their dovetail/boxjoint jig. See attached pic.
According to the owners manual for a Sears 315.17490 router,the template guide bushings is part #9 25079. See pics
I noticed on eBay two recent auctions for the above set of Sears guide bushings.
http://cgi.ebay.ca/ws/eBayISAPI.dll?ViewItem&rd=1&item=170028825705&ssPageName=STRK:MEWA:IT&ih=007
http://cgi.ebay.ca/Craftsman-Templa...ryZ20781QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
Needless to say, the Sears guide bushing are a pain to change as you have to unscrew the 3 screws to change guides and the guides are steel not brass which can cause damage to your bits if not perfectly centered, as I found out. They are also deeper in depth and designed for their dovetail jig or lettering guides and not versatile for use with 1/4" thick pattern templates.
Options, for using guide bushings would be to change bases either to a universal sub base such as Vermont America #23458 Router Guide Bushing Kit w Plate (also steel bushings)(see pic) or go with a Oak Park 7" x 7" sub base that accepts 1 1/2" brass guide bushings. Bushings are available from either Oak Park or Lee Valley depending on your preference.
Oak Park should have a sub base that fits your router as you can see from the following table. See pics
Oak Park sub Base plates
Base Plate Type A Product #BP012 7” plate with 1 1/2” center hole
Craftsman models
917574 315.17381 315.245070 315.27500
917506 315.17400 315.248851 315.27505
917507 315.17460 315.248862 315.174710
315.24886 315.275061 315.174921 315.244750
315.275082 315.17491 315.17470 315.174321
315.275110 315.17500 315.175060 315.175070
315.175040 315.17571 315.17551 315.248870
315.245900
Base Plate Type B Product # BP013V 7” plate with 1 1/2” center hole
Craftsman model 315.248700 (RE600)
Base Plate Type D Product # BP0457 7” plate with 1 1/2” center hole (no mounting kit)
Craftsman model 315.245000, 315.247000, 315.248870, 315.27500 315.27508, 927508, 925483
You will find that a 7" x 7" sub base is much more versatile to use and will give you better control and balance while routing and if you decide upgrade to the Oak Park table system the 1 1/2" bushings will be inter-changeable with the other plates available.
I hope this info helps you find either the correct bushing set or opens up your available options.

Ric
