The Stacking 2 technology stacks Small Parts as "Iron Gear Wheel (stack of 5)."

+1

temporary fix is to add this to data-final-fixes.lua :
(replace 400 with 100 if you have different config of main stacking mod)

if mods["pypetroleumhandling"] then
    if data.raw.recipe["deadlock-stacks-unstack-iron-gear-wheel"] then
        data.raw.recipe["deadlock-stacks-unstack-iron-gear-wheel"].results = {
            {type = "item", name = "iron-gear-wheel", amount = 400},
        }
    end
    if data.raw.recipe["deadlock-stacks-stack-iron-gear-wheel"] then
        data.raw.recipe["deadlock-stacks-stack-iron-gear-wheel"].ingredients =
        {
            {type = "item", name = "iron-gear-wheel", amount = 400}
        }
    end
end