Taking apart a NM hood assembly for a M-14 / M-1A / M-1 Garand is not recommended, because it is difficult to re-assemble without losing or damaging some of the internal parts.
You want to change aperture size without having to change an elevation rack that exactly fits your rear sight base, or You have already disassembled your sight and are stuck, or you want to have a spare parts kit in case your sight dis-assembles itself during a match, here is a rebuild kit which includes spares of the critical and easily lost parts, plus an assembly tool to help get the rear sight hood back together without damaging the spring clip.
NOTE: ShootingSight LLC makes no warranty as to the suitability of this kit for any purpose, nor does it warrant that you will be able to rebuild your rear sight without damaging it. If you are not competent or comfortable working on a rifle, or on rifle parts, bring them to a qualified gunsmith to have the repairs made.
If you are attempting to work on the rear sight while it is attached to the rifle, or if you are disassembling the rifle to remove the rear sight for repair, always be sure the rifle is unloaded before starting work. It is recommended that you wear safety glasses when working with this kit, as small parts are under spring tension and can unintentionally shoot off the work piece into your eye. Included in this kit are four detent balls, four C-clips, two thrust washers, and an assembly tool for the C-clip (you will need to re-use the 2 detent ball springs in the hood).