Target specific descendants only?

I have a script that finds a folder that contains a model of a grappling hook. It's supposed to only change the transparency of descendants whose name are "Union" "a" or "b".

local descendants = game.Workspace.grapples.grapple:GetDescendants()
for index, descendant in pairs(descendants) do
    if descendant:IsA("BasePart") or descendant.Name == "Union" or descendant.Name == "a" or descendant.Name == "b" then
        descendant.BrickColor = BrickColor.new("Really red")
        descendant.Transparency = 0
    end
end

Obviously the script doesn't work because I'm not changing what "descendant" refers to, I'm only changing the if statement so all parts in the model become visible. My question is how can I target only the descendant with those specific name?