ive tried putting verneer gauge in the pedal holes in both my cranks it reads 14mm in the xtr an 12mm in my sugino crank (this takes 9/16 pedals)
i have just found the bottom bracket bolt for the xtr bb actually fits ( screws in) the pedal thread too
acording to google an 1/2 plumbing pipe has an od of 15.8mm so the logical explaination is 1/2 pedals will fit these cranks
As Stevet1 said earlier, 9/16" is larger than 1/2", so if a standard pedal rattles around, a 1/2" will be even rattlier!
1/2" OD plumbing pipe... OD means Outside Diameter... doesn't really help.
Throw up a picture of the thread/crank.