FlatBoy! At our shop, all shapes matter! And we think it's a shame that there aren't enough squared-off shrouds for retrofitters working on rectangular reflectors (say that 3x fast!). The all new FlatBoy shroud rocks a 3-sided Type II white/amber switchback light pipe on the front that's extremely bright thanks to its BMW-like optics. Not only that, but they also incorporate a "dim" white trigger for perfect DRL functionality.
In Comparison: Don't make the mistake of thinking all shrouds are created equal. Even though less expensive alternatives may be available elsewhere: Morimoto shrouds are made from the highest quality plastic and have by far the most durable metalized chrome finishes. The cheap-o's out there are flimsy enough to deform from the heat just a 35W HID bulb, and their chrome finish easily flakes off.
Mounting: Centric Rings are not included by default, but are highly recommended to improve ease of installation on many projectors. The Centric Rings are simple reducers that clip into the shroud to reduce the inside diameter, making them more of a "press fit" onto the lens holder of the projector. JB Quik Weld is also recommended in order to prevent the shrouds from vibrating loose over time.
Trimming: Please note that trimming shrouds is a common task when retrofitting. Whether required to clear part of the projector, or fit within the geometry of your headlight housing; it's normal. Luckily, they're made of plastic - making that easily possible. We recommend a Dremel hand tool with EZ Lock cutting wheels to make the job easy.