How Different do Meta Descriptions have to be?

I'm doing product SEO and I have 3 products that have the exact same function but with a different spec in their name (e.g. Ripsaw 30hp, Ripsaw 50hp, Ripsaw 70hp).

If I were to copy the meta description over all three but change the spec, would that be enough to dodge the penalty for duplicate content or would I have to have totally different meta descriptions?