Bricks

Bricks are a currency originating in Scrap Clicker 2 and were later introduced in ScrapTD. In Scrap Clicker 2 they are used to buy some upgrades while in ScrapTD they are used for buying and upgrading barrels and defenses.

In Scrap Clicker 2
Unlocked at x15 Stars, Bricks are passively accumulated. Starting at 1 per second, production can be permanently and repeatedly upgraded in the following ways with all multipliers stacking:
 * Upgrading overall Star multiplier: x4 multiplier
 * Spending levels: multiplier *
 * Upgrading "More Bricks" upgrade by spending Bricks: x1.25 multiplier
 * (40+ Stars) Purchasing specific upgrades in the Skill Tree: multiplier
 * (105+ Stars) Upgrading the scrapyard v4: x1.5 multiplier/level

* Levels required increase by 1 every time production is increased by this method, however this can be lowered by purchasing the appropriate upgrades in the Skill Tree.

Upgrades
Each upgrade's cost is multiplied by 4 with each level.

Brick Multipliers
Once the player has achieved the top Golden Scrap Multiplier, they begin earning Brick Multipliers (if they are above the Barrel 103):