Twin row caged ball bearing. Fitted to Model 30M/40M (Manx) SOHC engines in original C3 looser fit, from good quality SNR manufacturer.
This is the twin row bearing fitted to the timing side of SOHC magnesium crankcase M30/M40 (i.e. pre-Featherbed) Manx models. It is different to the aluminium crankcase International models timing side bearing (which is only a single row bearing) - making the M30/Manx models stronger in this important area (which may explain why pre-featherbed M30/Manx magnesium crankcases are often found with the drive side crankcase damaged but timing side ok).
Original bearings had steel/bronze cages, but have not been available in that form for many years. Modern versions of this bearing are now supplied with a nylon cage. This is the correct looser fit 'C3' bearing as fitted to original models - but bear in mind the cage is nylon when soldering the whitworth screws over the bearing retaining plate - particularly if using a blowtorch, do not get the heat too close to the cage!
Update October 2019: These are a slightly cheaper brand of this twin row bearing than the SKF brand (Item 0022). We have a small quantity of these SNR brand bearings, with the same C3 fit. I spoke to my bearing supplier (a very experienced long term commercial supplier of bearings) who confirmed that these are also a good quality supplier - despite not having the same brand reputation as RHP/NSK/SKF etc. I only have a limited quantity of these bearings left - but as sometimes the SKF version go out of stock, these are an alternative if you are less concerned about brand - construction and finish look virtually identical to the SKF version