Purpose of this? Thanks!
It looks like something glued to the block that is/was used to secure something pushed onto the stem and held there by the “locking” washer…just a guess.
Its a duct pin to hold insulation on to metal duct work.
Such as rigid insulation board.
Yep, I used foil faced both sides and just adhered that to the blocks with adhesive.
Yup, that is the common method to attach, but in areas with high humidity, the cool block/concrete walls often get wet from the air laden moisture. The slight separation off the wall when using the shown fastener (or added spacer) helps the situation.
Now they use mechanical or power fasteners. Like they use on Dryvit systems.
But those glue on pins work well for home owners insulating their basement walls.