In one classic study, the diamond push-up (aka triangle push-up) was found to be the most effective exercise for activating the triceps brachii!
How to PROPERLY Diamond Push-Up (Close Grip Push-Up) For Muscle Gain
Pushups for Triceps: 8 Moves to Strengthen Your Arms, Chest, and
Proper Diamond Push Up Form to Build Your Triceps
Diamond / Pyramid / Triceps Push-ups / Pushups
Diamond Push Ups Benefits and the Muscles They Target
Push-up - Wikipedia
How To: Diamond Push-Up
14 Types of Push-Ups—and How They Help You
16 Push-Up Variations to Strengthen Your Upper Body for Fitness Level
How To Do A Push Up With Perfect Form - BuiltLean
Knee Push Ups Form
6 Different Kinds of Pushups and Their Benefits