By Martin Bayfield - Former England and Lions Second Row
And height is also useful, particularly in the number five shirt.
Their basic roles are the same as the number four - to secure possession and, as with all the forwards, to tackle tight into the set-piece and the breakdowns.
At the line-out, the taller second row (usually wearing the five shirt) tends to be the number four-jumper.
A ball thrown to him has got further to travel and is obviously in the air longer than it would be if it was aimed at the two-jumper.
So the four-jumper has to deal with more variations in the air - you can either go forward, straight up or backwards.
But with the way the game has changed, players regularly shift around positions as the line-out is thrown.
The days of jumping in your one position are over.
There's a lot of movement, a lot of deception and a lot of dynamism and that's very different.
In the scrum, the taller second row may be the loosehead lock, which is on the left side of the scrum.
The loose-head tends to move more - he's only bound in on one side, so his left hand is loose, while the tight-head is tightly bound in and pretty stationary.
The Ruggas 2017 Drafts was done as shown below.
Quagga - Carl Els (Affies)
Shawn - Justin Sadie (Menlo)
BMT - Pierre Pretorius (HJS)
Sabbat - Xavier Haupt (Bellville)
Hooit - Louis Meiring (Outeniqua)
Kattes - Ruben Kotze (WK)
Charl - Aaron Brody (Queens)
Beet - Ollie Calvert-Evers (MHS)
Louis - Breyten Maritz (Paul Roos)
Carl - Elrich Louw (Transvalia)