From Brickipedia, the LEGO Wiki

Pegs are TECHNIC components which can fit into TECHNIC holes (such as those on either side of bricks or beams) and are used for holding pieces together.

The first peg, part 3673 was introduced with the Expert Builder (now TECHNIC) range in 1977.


High friction[edit]

Pegs with friction1.png
Picture Part Introduced
4459.gif 2780 (formerly 4459) 1982
4514553.jpg 6558 1993
4206482.jpg 43093 2002
6089119.jpg 18651 2015
6015356.jpg 11214 2014
6628black.jpg 6628 1996

Low friction[edit]