Mechanical

The Sims
The Mechanical skill allows a Sim to repair broken appliances, electronics, sinks, tubs, toilets, and showers at a faster speed which may eliminate the need of a repairman. The skill also reduces the risk of electrocuting themselves when changing light bulbs, however, a maximum level Mechanical skill (10/10) does not eliminate the risk of getting electrocuted. Mechanical skill is also important in the promotion of the Sim's career, including (but not limited to), business, military, science, and law enforcement. In Makin' Magic, a Sim's Mechanical skill affects the number of charges charms they make will have, and how many MagiCoins they'll get for performing on the wooden stage in Magic Town.

To increase Mechanical skill, have your Sim read mechanical books from the bookshelves. In Livin' Large, a Sim can use the woodworking table and make gnomes to increase their Mechanical skill. The higher their Mechanical skill, the faster they make gnomes and the higher the price each gnomes can be sold for. In Makin' Magic, a similar table, the Kraft-a-Gargoyle table is introduced, which also increases the Mechanical skill. In Makin' Magic, Sims can also increase Mechanical skill by using the Prick-Me-Not Spinning Wheel.

The Sims 2
This skill is mainly used to repair things and also in different careers. A Sim's mechanical skill determines the chance of getting electrocuted when attempting to repair a broken object. It can be studied by a book, by repairing broken items or by purchasing the "Jimmy three fingers" rocket bench (console only).

If you have The Sims 2: Free Time installed studying the mechanical skill from a book will increase your sim's enthusiasm for the Tinkering hobby. You also get a broken down car which trains your mechanical skill while you repair it.