i recently bought an old 1981 apollo custom sport and i need to install a new bottom bracket. when i was looking at the bottom bracket shell i noticed that it had metal pieces at either side of the shell which have many grooves surrounding the inside of the shell. these pieces are a part of the frame and can not be removed. the old bottom bracket would have had tiny metal protrusions which would fit in with the grooves. i was just confused if this frame needs a specific type of bottom bracket or if any normal bracket would do. any help/information would be greatly appreciated

thanks

Those are threads in the shell itself. You'll need to find a bottom bracket with matching threads (possibly English) and a spindle width to match your crank needs.

If you don't have the correct tool, nor any way of figuring out the threading by searching online. Take it into your LBS and have them check the threading. They may sell you a decent quality BB to go with it.
-Gene-