Are you talking about the Magna Hoop and the Snap Hoop? They have a magnetic frame that fits inside the regular hoop and plastic templates. You place the fabric between the magnetic part and the plastic template and secure it with 4 magnets with the Magna Hoop. The Snap Loop is magnet on both the bottom frame and top frame. I had the Magna Hoop but sold it. Just didn't hold the item tight enough even on thin items. I want to try to Snap Hoop because it seems to have a stronger magnet but it is about $180.00
According to Designs in Machine Embroidery magazine and some dealers, I was told the magnetic strength was not enough to harm the computerized components of your machine. But I was also told that the magnetic pin cushion shouldn't be used near the machine!!