Per the Yates Website:
"Function: Shock absorbing sling designed to reduce peak loads in any climbing system!!
* Multi-functional energy absorbing device. Screamers will provide added protection in climbing and rescue situations. Screamers not only absorb energy directly because of the stitch ripping effect, they also allow your rope to absorb more energy from the fall by increasing the time interval of the fall. Screamers can reduce shock loading in any rescue system. The standard Screamer can effectively reduce peak loads by 3-4kN in any climbing or rescue system. YATES original Screamers were first developed over ten years ago, YATES has since developed numerous variations on the Screamer design for use in Aerospace, Military and explosive testing for the deceleration of objects. Screamers were originally designed to be used on less than ideal climbing protection such as small nuts, old 1/4" bolts, snow anchors or marginal protection. We have determined that the most effective activation for a standard screamer to be >2kN(550lbf.) for climbing related situations"
*Standard SCREAMER, SHORTY, ICE-SCREAMS:
Activation: >2kN. Reduction in system peak loading 3-4kN. Runner Strength: 26kN.
* ZIPPER Screamer: Activation: >2kN. Reduction in system peak loading 4-8kN. Runner Strength:26kN.
* SCREM AIDS: Activation:>1.5kN. Reduction in system peak loading 1.5-2kN. Runner Strength: 7kN. "use on extremely marginal aid placements only"
Personal ExperienceI use my SCREAMER's in all AID situations with marginal PRO, especially in questionable small heads, thin pin & Beak placements. I have zipped on several occassions and the SCREAMER worked as advertised. I also will employ them on Ice Climbs where marginal screws and on Trad Pro that just may need the extra uuumpf to back up the Pro. They work!