This is a 3d printed slip over guard made from aquarium safe PETG plastic. PETG will not leech harmful chemicals into your water, and is more durable and heat resistant than other plastics. Easy to install, simply held in place by the wet end magnet. Intake holes are 3mm with an open exhaust to promote better flow. 3d printed items may have visible layer lines or minor imperfections such as stringing, blobs, or other blemishes. These do not affect functionality.