old uk rebar marks

huangyhg

old uk rebar marks
i have a set of reinforcement drawings (uk deisgn) giving bar marks (sizes) as m5, m7 etc. the drawings are from '60s. could anybody help in deciphering what bars are these.
thanks in advance.
if memory serves me right (and please do verify), the 12 is the diameter in mm. i believe m designates mild steel bars. higher strength rebar had the letter designation y.
anyone familiar with the old cp 114(load-factor design) and 110(limit state design) will be able to assist you.
henri2 is correct.
it was common to designate m for mild steel bars ( hot rolled mild steel bars to bs 4449 yield stress 250 n/mm2) and y for high yield (usually hot rolled high yield of 410 n/mm2),  still is in fact, except the yield strengths may now differ. a little puzzled by the m5, m7 types though as these would not be common diameters ( usually m6, m8, m10, m12 etc).
thanks for all replies. our thought here is that it must be in imperial units (1960's) so could it be in 1/8 of an inch (i.e. 7m - 7/8inch mild steel).
just a small corrections that the bars are annotated 7m etc, not m7.
i'm based in the uk. i've seen lots of old rebar drawings. i don't recall seeing m designations!
current uk practice is to use t for high yield steel and r for mild steel.
older practice (1970's)used the letters y and r.
even older drawings tend not to be consistent, but generally did not utilise and letter reference for 'ordinary' bars.
in the 1960's very little high yield steel (in the form we understand) was used. various cold worked bars were available with differing properties. it is possible that the building in question features some of these. the more common tyes were square bars twisted on length to form a kind of helical rib and serveral variations of multi-strand wires.
such reinforcing can be a real problem - i've never had much luck with searches for contemporary design guidance - may be another poster could help?
you don't state when in the 1960's the drawings were produced. in the early 1960's imperial units would be most likely. this changed progressively such that by the mid 1970's metric would be dominant. imperial prevailed until the late 1970's in domestic type construction. re-bar manufacturers would have changed over to metric sizes (i guess) in the early 1970's.
metric bar sizes, as xxpegasus11 states, are 6, 8, 10, 12, 16, 20, 25, 32 and 40mm diameter.
can you conduct a survey and do some opening up to expose the reinforcement?
pba,
you have jogged my memory and i concur with your historical account.
could the m5, m7 possible be bar marks that relate to a reinforcement bending schedule in the working/placing drawings?
just to clarify further, the whole bar annotation includes (i guess), a number of bars (confirmed by counting them on cross sectional drawings for several examples), xm (?), bar mark for bending schedule (in brackets on drawings) and bar spacings, so typical one would look like:
42/6m (113) 12"
we cannot expose the bars because of the nature of the structure.
bkal,
you may have to lay your hands on a copy of the british standard that dealt with standard practice for structural engineering drawings(bar scheduling etc) of that era because i am sure bs 8666:2000 will not work for you.
i had it confirmed from other source that it is indeed in 1/8ths of an inch, refering to  bs 1478: 1967 (bending dimensions and scheduling of bars for the reinforcement of concrete).
thanks everybody for their contributions.