If you have a Speedplay Grease Gun and use it only to lube the spindles on your Speedplay pedals, chances are good that one cartridge of grease will last you a lifetime and beyond. However, the Synco Super Lube that comes with the grease gun is good for just about everything that has moving parts and requires grease.
So eventually you may need this Speedplay Grease Gun Refill. It's a 3oz tube of Synco Super Lube that gets housed inside the grease gun handle. Super Lube is a multi-purpose synthetic grease with PTFE (Teflon) particles in suspension within the grease. Because it's synthetic, it's exceptionally pure, stable, and predictable. It's superior to standard petroleum based lubricants, and you can use it on your pedals, suspension pivots, hub bearings, etc. Super Lube is waterproof as well.