I got this and another one (each end of the scope had different sizes) to replace the bikini cover that came with my Bushnell scope. I was tired of keeping track of the bikini covers and keeping them clean when off the scope, so these were a logical purchase. Just to be sure I was getting the right sizes, I double checked Butler Creek's website for the sizing chart and I used a Vernier caliper to measure each end of the scope. There is also a sizing sheet you can print out to help determine what size you need. I read at one point that they recommend rounding down a size if your scope is in between their sizes available. I had to do this on one of the covers and it worked perfect.

Once installed on the scope, they work great. Covers slid on nice and snug, they stay in place, and flipping up the cap is quick/easy. I'm honestly looking at getting these for 2 other scopes that I have. Also, you got to love the price for them.

I already have one set of Butler Creek scope caps for my rifle scope which is a Leupold 4.5-14x40mm. I've had these scope caps for nearly 20 years with no faults whatsoever. I upgraded my muzzleloader scope to a Leupold 3-9x40 which meant I needed new scope caps. I went to Gander Mountain (the only local dealer that has Butler Creek products) but they were out of the sizes I needed. The size 13 flip open is the perfect size for the eyepiece. Size 26 flip-open is the perfect size for the objective lens. These sizes fit both of the scopes I mentioned. Butler Creek has a chart on their website that was accurate which can be found here.
[...]You can find your scope make and model starting on page 4 which is super helpful. As stated, the chart was accurate for my Leupold scopes. If you still are unsure, I would suggest going to a local dealer that carries Butler Creek products and confirm the size that way.

After trial and error and purchasing the wrong cover multiple times I have finally found one that works for my scope. The size 10 eyepiece cover is a perfect fit for a Nikon Buckmasters II BDC 3-9 x 40 scope. Don't go by what is on the Butler Creek size chart or you'll do what I did and buy a couple of the wrong sized eyepiece covers before finding one that is the correct size. A nice snug fit, wasn't hard to put on, but you would have to be trying to remove it to get the cover to come off, it's not going to pull off if it gets snagged on something.

These seem like a great idea, but at first I didn't order them because getting the right size looked like a hassle. I wasn't sure the convenience of the flip up covers was worth the potential hassle of ordering covers that don't fit. Then I noticed the "Check the Butler Creek Scope Cover Fit and Sizing Guide" note on the product page (with a link to the guide), so I figured getting the right size would be easy after all. I purchased eye and objective covers for a Nikon ProStaff 3-9 x 40 Black Matte Riflescope (Nikoplex). According to page 9 of the sizing guide the correct Eyepiece cover size for a Nikon ProStaff 3-9 x 40 is size 11.

I just received the covers today and unfortunately the guide is incorrect; the cover is far too small. Going by the size of the Eyepiece OD (1.73 inches) on the scope's product page I'm guessing the correct size is 19 (1.73 inches). I had the same problem with the sizing recommendation for the objective side cover as well; the guide suggested a size far too small suggesting a size 28 where it looks like maybe it should be a 31.

It looks like Amazon will only refund my money for these and I'll have to pay for separate shipping to purchase the (hopefully) right size covers. I asked in my note for them to replace it with the right size, but I'm not sure they will do so. This leaves the question; if I can't trust the Butler Creek sizing guide linked from the page, can I trust the other sizing instructions from Butler Creek on this page?

The Butler Creek Flip-Open Objective Scope Cover, Size 02A is great fit. Spend all this money on a scope you are going to want to protect your optic. Fit's the Burris MTAC Rifle Scope 30mm Tube 1-4x 24mm perfect. The cover has a fast flip up and it goes 120 Degrees I would prefer a cover that flips all the way back but it will protect you scope