Dr Plumbs 6mm Filtered Smoking Pipe 4407-9606 The Dr Plumb 6mm 4407-9606 is a traditional, bent pipe with the ever comfortable Apple shaped, Briar bowl, which is designed for use with the 6mm absorbent filters. The Dr Plumbs 6mm range are based on more traditional shapes and sizes, with good thick walls and a reasonable length, which prevents overheating and helps provide a cooler more enjoyable smoke, which isn't found with smaller pipes.