A clamping lock is provided for use with a looped tie in a form for settable casting compositions, such as concrete, which lock is provided with protrusions on each of a pair of clamping members to fit into aligned connector slots of a pair of rails of adjacent panels of the form to properly position and firmly secure the lock to the form. The securing of the clamping members on the rails also holds adjacent panels of the form together. The rails are provided with tie notches which when panels are placed side by side and properly aligned the tie notches form tie slots through which a tie having loops at each end can be extended between panels of opposing sides or walls of the form structure. A tie opening is formed in the clamping lock through which the loop of a tie is adapted to extend. An anchor lock having a tapered arm is mounted on the clamping lock so that its arm can enter into a tie loop extending through the tie opening to secure the tie to the clamping lock and to tension the tie. Various means are provided to secure the clamping members against the rails.