I think a link should be permitted as an example. It shouldn't be the primary element of the answer: in the example from the question,
Use one of these
I think by itself that wouldn't be an answer for the usual reasons of linkrot and "your answer is in the next castle". But
You should use a drill guide, as that will simplify your process by holding the drill in place and showing you where you are going to make your incision. This drill guide for example has [some list of features that is helpful].
Would be okay - if it contributed significantly to the answer.
The important part, though, is that the answer stand without the link, just like any other link; it can only be used to suggest context or expand in detail that is beyond the scope of the written answer. I think in a lot of cases - like this - it's not needed; you can explain what a drill guide is without linking to a particular product. I would only use it here to compare/contrast between different ones.