a spreader function as may be best seen in fig3 slit 54 is narrower at its forward end in order that cone 30 will serve to obturate the slit and prevent egress of wet concrete and moisture from the form the semicircular relieved portion 56 of bore 57 provided in the rear end of seal 34 is to accomodate the tie rod button not shown when the seal is axially at its rearmost position on the rod a ramp shaped projection or bossed portion 58 on the tie rod with a larger diameter than seal bore 57 causes the seal to expand due to slit 54 or similar accomodation depending on resiliency of material used to sealingly engage bore 22 when the seal is in place in the form bore as shown in operation the tie rod with cones thereon is inserted through one of the form bores and positioned so that the lower edge of the cones overlaps the form the seal 34 is then moved laterally onto the rod 26 so that its accomodating bore 57 receives the rod the seal is then advanced axially on the rod until it abuts the cone 30 and is sealingly engaged within the bore 22 by.