Rear sights bolt right to the barrel assembly. Personally I'm a big fan of a rear aperture sight. Williams makes an airgun version that isn't too expensive and you'll notice your iron group sizes shrink VERY noticeably
They also make pretty much my all-time favorite rear sight -- a cooperative venture with Crosman, if I'm not mistaken. Unfortunately, it's fairly costly right now at around $70 to $90, but it's known as both the Crosman-Williams and/or Williams Notched Sight. They're available at Pyramyd Air, Amazon, and probably just about any 'site with Crosman add-on/modification gear. The Notched system looks and works a lot like their excellent peeper version (I have the peeper on a couple of my air rifles), but I prefer the Notch over the sometimes hard-to-see peeper by a very wide margin and consider it about the best third-party, DIY, adjustable rear sight available. It pairs almost perfectly with the cheap plastic Crosman front blade sight that's stock, glued-on equipment on their 1377/1322, 362 and other Crosman airgun models, as does their somewhat egg-shaped, black, silver or brass muzzle brake/front sight with the small, round upright 'post,' often seen on the Crosman 2240 CO2 and other Crosman airguns. I bought and mounted a Crosman/Williams Notched rear sight on my 1300KT carbine the wife gifted me from the online Crosman Custom shop (the rifle was a steal at just a hair over $200.00 delivered!) and that was all she wrote for me! Luckily, it's extremely easy to install on Crosman airguns equipped with their metal breech, such as those made for the 13xx series of air pistols, the 362 carbine and other Crosman models. Hey, even I managed to do it a few times, and I'm more mechanically DEclined than inclined, I'm afraid. ;-) Both Peeper and Notched models are exceptionally nice sights, super-easy to dial-in for fine accuracy and both are a breeze to install with simple hand tools (just a small screwdriver, basically, if I remember correctly). Really, it's just a matter of whether the shooter prefers a peep sight, or a notch/blade system. When I hit the lotto (or some other, equally likely, here-ya-go-have-a-big-pile-of-money windfall), I'll install a Williams Notched Rear Sight on any and all of the airguns in my collection capable of utilizing it. It's absolutely a well-made, quite good quality piece of add-on gear.
Pictures below, the first as advertised on Pyramyd Air and the second from a photo of the first one I bought, mounted on my awesome, custom-built Crosman 1300KT .177 caliber carbine pumper named "Evie"