Comments about American Aldes 8" Galvanized Steel Roof Cap:

This product has fewer flow restrictions than most caps for 8" round duct to support higher cfm. The B634 cap has a plate in the throat that I wanted to avoid. The screen is not removable, like B634, but it is more secure and could be cleaned in place if ever necessary. The corners of flashing arrived slightly bent, but was easy to rebend. (The B634 from a different retailer that I returned also arrived slightly bent.) The 4" long adapter made connection on inside easier, but it also meant loosening more shingles to get the flashing under the top and side rows of shingles.

Comments about American Aldes 8" Galvanized Steel Roof Cap:

Bought this product to replace my highly restrictive builders type roof cap for my kitchen stove fan. The roof cap's base flashing is small which allows for easy installation. If installing on a wood shake roof, leakage from rain water is highly probable due to its small base flashing. Best bet, hire a roofer unless you know what you are doing.
Overall, the roof cap is big but it's not streamline like some more expensive roof cap of its type. "It does work quite well". Previously, when we cook the fan could not expel most of the odor and fumes from our cooking. So the fumes would scatters all over the entire house. Causing the house to reek of what we've just cooked. With this new roof cap, air flow is so much better that our house no longer reek of our cooking. "You must also have a good stove fan to accompany the roof cap."
Besides the roof caps low flow restriction, the flapper will close to prevent insects and debris from entering the system when it's not in use.
I'm not sure I wood recommend this product due to its small base size resulting in potential roof leakage. If the roof cap is rated purely on it's performance and nothing else, then this is a good roof cap to buy.