UKC

I recently visited The Boardroom near Chester (amazing wall! well worth a trip) and noticed they have letters on their lower grade rope routes (4s & 5s). I found it slightly odd as most (all?) walls I've been to in the UK have no letter on these low grades.

Looking at the grade comparison charts etc, French/Sport grades have the letters on the lower grades (i.e. 4abc(+), 5abc(+), 6abc(+), 7abc(+) etc). The only thing that seems to match the system I've seen in most walls (at least around Greater Manchester) is font bouldering grades (i.e. 4(+), 5(+), 6abc(+), 7abc(+)). But those roped routes can't be using bouldering grades, surely? Do UK climbing walls use sport grades but omit the letter on grades lower than 6a? Or are they a different system entirely? I'm pretty sure I've always heard them called "sport" grades. The Boardroom have confirmed they use sport grades on Twitter.

Yes.

That's just an old-fashioned version of normal French route grades.

It may be that getting an accurate a,b or c grade at the lower grades is hard and mostly irrelevant (especially with some of the grade variance I've seen in the 4's and 5's) so they don't bother. Do they use '+'s for the 4s and 5s?

Definitely seen 5+ in most gyms that don't use letters for 5. Think I've seen 4+.

Outside I've only really seen french (sport) grades, 4,4+,5,5+,6a etc. At the walls round here they grade abc in the 4s and 5s too. I've been told its to provide people with a sense of progression through the grades but in my view trying to split 4s and 5s into abc is basically meaningless.

For roped climbs many walls start using the a, b, c once grade 6 is reached. 

Using a + to split the lower grades 4, 4+, 5, 5+ etc.

Many continue to use the + along with the a, b, c as well so you might find 6a+ or 6b+