Mystery Theme #3 by PolinskyL

In pinball, it's an element that pushes the ball away on contact, usually with additional force. In pool, it's one of a dozen obstacles placed on a table with only two pockets. WHAT IS IT?

There are a plethora of examples of WHAT TOPOGRAPHICAL CONCEPT, for a space that resembles Euclidean space near each point, but not globally? It was part of the topic of the first original paper written by a mathematician who learned, in one word, the secret of success in mathematics from the great Nikolai Ivanovich Lobachevsky.

WHAT TOOL often uses a Vernier scale in order to make a more refined measure of thickness? It is also the term for the thickness of a piece of paper.

In the Northeast, the name might bring to mind a food company that sponsors a blimp at Red Sox games; in the Northwest, the Beaver State's tallest peak. (Let's not talk about the word's association in the South.) WHAT IS THE NAME?

WHAT SEVEN-LETTER TERM for the pitcher and catcher begins with the name for a piece of equipment neither of them is using?

Perhaps due to its roots in Fullerton, CA, WHAT GUITAR MAKER was associated with surf music giant Dick Dale (as well as the rather less surf-focused Jimi Hendrix, Yngwie Malmsteen and Eric Clapton)?

A chiton has 8, a heart has 4, and a mussel has 2 of WHAT?

Girolamo Cardano was, as Wikipedia tells us, "an Italian mathematician, physician, astrologer, philosopher and gambler". He is also credited with describing WHAT TYPE OF CYPHER, which uses a sheet with holes in it to write a coded message onto a second sheet?

NFL helmet logos are a virtual cornucopia of aggressive iconography (except, perhaps, for the Browns). WHAT weaponlike FEATURE appears on exactly four helmets, two NFC and two AFC, one each from a North, East, South, and West team?

The Boudin Bakery in San Franscisco has reportedly been using the same one of WHAT for over 150 years?

In 2014, Nordstrom acquired an online business which pairs customers (primarily men) with personal stylists who select a monthly package of clothes for them; WHAT IS THE NAME OF THE PACKAGE, which is reminiscent of a one-off 'show' associated with the bridalwear industry?

If you've managed to navigate the previous eleven clues, you may be able to figure out a common theme. WHAT IS IT?