These glass dildos are called “juicers.”
Here is how they work. First off, this needs two people - the woman getting juiced and her lover doing the juicing.
You lube up the shaft and especially the bumpy wheel - the side with all the bumps.
Next, the lover lubes up their fingers and the “handle.”
Insert the dildo into the woman until the outer wheel is pressed up against her clitoris.
Once properly placed the large end will be resting up against her G Spot and the wheel section will be pressed against her clitoris.
Now that it is in place, the lover starts cranking the juicer handle with their fingers. It may take two hands to keep the wheel up against the clit.
Start out slowly and adjust your speed to match her arousal and “juice level.” These can produce a phenomenal amount of wetness from the vagina. Sometimes I have had the girl squirt for the first time just from using the juicer.
I first saw this on HBO’s Real Sex special. The best ones come from Glass Fantasy.