The Snap to Primary (SNAP PRIM) order is similar to a pegged order, as the original order price is determined by the current bid/ask plus or minus an offset. But unlike the pegged order price, the "snap to" order price doesn't continue to peg as the price moves.
A Snap to Primary BUY order snaps to the bid plus the offset to set the order price. A SELL order snaps to the ask minus the offset.
To create a Snap to Primary Order
Create a buy or sell order.
From the Type field select SNAP PRIM.
Specify an offset amount that will be added to the bid (for a buy order) to determine the limit price.