These chunks of 0.1" header have an extra pin row, so it's handy for when you want to connect cables that come in sets of three, like perhaps sensors, or servos. These plug into any standard 0.1" spacing perf-boards or other PCBs and work nicely with Female Ended Wire Sets. Each purchase consists of four header pieces. Each header piece is 3 rows by 4 rows. You can stack these next to each other in any direction. We think these are a great addition to our 16-channel PWM/Servo driver breakout, so we have a photo showing them installed!