On page 6 of the link is the fitment guide for Triumph bikes. These are Slipstreamer windshields. I ordered the SS-30 in 17" to fit my America. At Chromeworld's website the actual model number is SS-30-17CV, the CV denoting the larger size clamps to fit the large fork tubes of the America. I'm assuming they are the same on the Speedy, but not certain.
I ordered this one because it fits to the forks, not the handlebars. Most of the cheap ones you will find have clamps that attach to your handlebars. Some like those, some don't. I wanted to keep my bars clear because I may add other items to them later. When I ordered it the cost was $189.99 USD plus $7.99 shipping.
Hope that helps. There are others out there, but this particular one comes in 17" and 20" heights to allow you to fit it to your personal needs. I'm 5'7" so I went with the 17".
http://www.slipstreamer.com/Slipstre...Chart-2009.pdf