That's a monster 55T chainring from the first generation Shimano Dura-Ace groupset of about 1975. I love the look of those old Shimano rings, and they match the FRM cranks nicely. Those run on a 103mm FRM titanium BB. Pedals are also a favourite - Shimano's A515, which have been obsolete for over fifteen years. Luckily, good pairs still turn up regularly on eBay.