Blue Racer/Wolverine makes a solid lifter that from the outside looks like a hydraulic lifter - but is actually a Solid lifter. If theres no spring and plunger inside, your lookin' at a solid lifter. I say that to a 99% certainty - however, I must allow for any new products in 2004 that I'm not aware of. I'm pretty sure BlueRacer has a website, they should have pictures and internal breakdowns of their products.