In its listing for this bow roller Vetus says it is suitable for rope/chain sizes up to 8mm and claw anchors up to 5kg. This item was purchased at Fisheries Supply in Seattle, but boat plans changed, and it was never installed nor otherwise used or injured. It has been protected indoors in storage since then. It looks and behaves just like new. This same Vetus item can still be special ordered from Fisheries for about $256. The photos here show this item mounted for demonstration and planning purposes to a piece of 4x4 held in a heavy vice.
The stainless retaining pin mechanism that is meant to hold a retracted anchor in place looks well designed on this roller. The nominal 8mm diameter pin measures 7.95mm with a Starrett caliper, but there is a small fixed non-retracting lateral stainless knob that sticks out on the distal end of the retaining pin and makes the pin captive in the starboard side of the rollers' frame and allows the pin to engage a notch in the port side of the rollers' frame. The spring under the knurled knob on the other end of the pin holds the pin and a compatible anchor in place. So with this little latching knob added to the pin's diameter, an anchor retaining hole of at least 9.15mm diameter is needed. If not planning to use a Vetus anchor in the specified size range, an interested boater should consider bringing his anchor along to try out and verify fit before purchasing.
The last several images are screen-saved from the current listing on Vetus.com with captions added by the seller to provide more complete and more accurate dimensions for interested boaters.