well i had to buy one of these SEF coils. 10x12 is what i bought. i did air test comparison,was alot deeper than the 9.5 and 6x10 DD. also alot more sensative to tiny items,gold ear rings,rivets,etc. compared 10x12 to the whites 9.5 in my yard....same settings several targets 10x12 gets good lock on and 9.5 doesnt make a sound...i had actually used the 6x10 in this 20x20 section of yard just off my porch..very nail infested due to being built in 1853 so lots of rusty goodies. been over this part of the yard alot with every detector ive ever owned and every coil.got no good targets with 6x10 or any coil for that matter until 10x12 sef. in that area within 15 minutes found a 1864 indian head penny and a 1936 buffalo nickel. both had great smooth tones and you could tell it was a good target with meter reading from 5c to 1c. dug 2 very old wheat pennies that the 9.5 did not make a peep on. with same settings. both of them were lock on 72-74 with 10x12.. also the weight of the coils is sef 10x12 1.3lbs with coil cover, whites 9.5 1.1lb without coil cover. so almost the same. sef is much smoother and deeper and separates better than even my 6x10 DD. i dont know how its made... but i do know its very impressive!! i have 2 MXT detectors that i was testing with..