As a general rule of thumb, oil filters come in two sizes. 2.5 in and 3.25 in. Of course this will vary to a degree, but it sounds like your K&N is of the longer variety. As for the "stock" size, I believe it to be the shorter version.
Some people go their whole life wondering if they made a difference, Marines don't have that problem.~ Ronald Reagan
2012 XCT, AFR+ Gen 4, Lloydz air filter. I don't equate noise with power.
I ride with the Force.