Have you ever had a rear wheel axle shift forward, causing the chain to lose tension and take your foot off the pedal?
The Surly crew has experienced this on all kinds of hubs and frames, and while there are many BMX-type chain tensioners out there, very few of them fit the drop end of a Surly frame without some shaving or other modification.
We designed a tensioner that would securely hold the rear wheel on a Surly frame end, as well as most other track type ends, and with a bit of a Surly touch, this tag nut tensioner can also be used as a bottle opener for beer and other beverages.
The wing-shaped bolt can be adjusted without the use of tools, and the two holes allow for a wide range of wheel positioning, front and rear. An aluminum adapter is included to change the axle diameter from 10mm to 6mm, allowing the use of quick-release axles in addition to BMX-type bolt-on axles.
Since you really only need this tensioner on the drive side, it is sold in units of one... But if you absolutely need it on the other side for balancing, you may be in luck that you can use the bottle opener on either side.