Trail Blazer Ultra Light 5.0L (6.5″) Item# 300-6.5

RAPIDPURE TRAIL BLAZER Ultra Light 5.0L/m 6.5″ Filter

• Replacement cartridge; Fits the RapidPure Trail Blazer gravity purifier and is easy to install
• Virus protection; Purifies water by removing 99.99% of viruses, bacteria, parasites, and more
• UltraCeram technology; Removes pathogens 100x smaller than those caught by 0.2 micron filters
• Fast flow rate; Ultra-fast flow rate purifies as it filters without any waiting or back-flushing
• Great tasting water; Activated carbons instantly remove odors and improve taste

It seems to me that you should know an Ultra Light 5.0 L/M 6.5″ filter is commonly used for gravity feed systems like this.