The odd thread in place between bolts, a bolt missing?

tasp05 ??/2014 AltLd
Steve Lewis 15/Sep/13 Lead O/S
with Isobel Nicholson, Joshua Lewis
Josh Lewis 19/Jan/13 Lead
with Isobel Nicholson, Neil Murphy
Swamp murphy 19/Jan/13 Lead
with Yosh89
Hidden 19/Jul/11 Lead
High 20
Mid 20
Low 20
High 19
Mid 19
Low 19
High 18
Mid 18
Low 18