From A.R.M.S.:

Raises the optic 1 1/2" and has a see-thru tunnel.
The A.R.M.S.® #54™ Throw lever® mount for the Eotech Holosight(and similar HUD type sights) raises the optic 1 1/2" and features a see-thru channel to allow the operator to view their iron sights in case the optic fails. *

*TM The distinctive shape, style, and appearance of the lever and lever platform on all A.R.M.S.® mounts, and the body of the #17® mount are trademarks of A.R.M.S.®

The additional height of the #54™ raises the optic high enough to be easily used while wearing a gas mask or shooting from a chest mounted heads up position.

Weight - 4.3 oz

*when mounted on a Swan® Sleeve or A.R.M.S.® SIR® system