Learn Russian: Пожалуйста, сделайте эти складки поменьше, а швы — покрепче. - Please make these folds a little smaller, and the seams a little stronger.

The prefix по- added to a comparative adjective softens its meaning, often translating as 'a little' or 'slightly'. So меньше means 'smaller', but поменьше means 'a little smaller'. Similarly, крепче (stronger) becomes покрепче (a little stronger). It also makes the direct command sound softer and more polite.

How do we get the form крепче from the base word крепкий?

Крепкий (strong or sturdy) is a common adjective with a one-word comparative form. The suffix drops, and the stem consonant -к- mutates into -ч-, resulting in крепче. While you could grammatically say более крепкие, the one-word form is far more natural for everyday requests and is required if you want to add the по- prefix.

Why is there an em dash (—) before покрепче?

The em dash replaces the verb сделайте (make) in the second half of the sentence. Instead of repeating the verb to say а сделайте швы покрепче, Russian relies on the dash to show that the action from the first clause carries over to the second.

Why are эти складки and швы seemingly in the nominative case if they receive the action of the verb?