Canon's original plastic-mount nifty fifty, iconic but fragile with five straight aperture blades.
The Canon EF 50mm f/1.8 II was introduced in 1990 and became the best-selling Canon lens of all time. Incredibly cheap and surprisingly sharp, it was the default recommendation for any Canon shooter wanting to try a fast prime. Its plastic construction earned it the nickname 'plastic fantastic' and occasionally less flattering descriptions.
Optically it is nearly identical to its STM successor with good sharpness from f/2.8 onwards. The crucial difference is the five straight aperture blades which produce pentagonal bokeh highlights that many photographers find objectionable. Autofocus uses a noisy micro-motor that is slow and not suitable for video. The plastic mount is notorious for cracking.
Canon EF mount only, 52mm filter thread. This was replaced by the EF 50mm f/1.8 STM in 2015 which addressed every criticism: metal mount, seven rounded blades, quiet STM motor. The Mark II remained on sale for 25 years with essentially no changes, a testament to its value proposition.
Still very common and extremely cheap used. The plastic mount is the critical check point as cracked mounts are common and irreparable. Also check the AF motor which can fail. At a few pounds more the STM version is a better lens in every measurable way. The Mark II is primarily of interest for its historical significance.