Omega Filter Holder for B-8

I see that BnH has an under-lens filter holder for B-series enlargers. However, their description doesn't say anything about the dimensions. Does anyone know the size of VC filters that fit? Or, the closest size (to cut down)?

- James

Do you not have the filter holder in the head?

Actually, I don't have the enlarger at all! Yet, that is. About to acquire one, though, and just doing some planning ahead as to what I'll need. I've done a bit of searching and haven't turned up such info at this point. I'll soon have more details in hand but was curious.
Related to your question, I did see a post saying that relatively few B-8's were supplied with a head that included a filter drawer. Apparently those models are very hard to come by. So, it appears I'll be needing the accessory holder and filter set.