I have used many different types of contour gauges over the years and this set is one of the best plastic sets I have ever used. The "pins" are thick enough not to deform when inserted. The curved locking lever locks everything very well. CONS: not easy to install. You usually have to wiggle it slightly when you press it to make the pins slide back. Steel sensors are usually much easier to advance, but are usually significantly more expensive. As with any set of outlines, I usually hold the probe in place once I've slid it into the shape I want, and then run my finger along the back of the pins and press them firmly into the shape I'm outlining before I they block sensor and pull it out.