Helicoil Shrinkage at Installation

Oddly, I designed a trade show display for my work and had M4 spec'd Helical Inserts to be installed. Gave a part number and all. When I got them the shop didn't put them in because they forgot to add it to the quote. I said, "no prob, done this before.." For the life of me and a coworker who is also an experienced car guy could not get a helicoil in. I bought 3 different brands, spoke to the shop and could not get them to work and finally found a brand that would. Now I design in Keenserts (or equivalent name brand stake-able threaded insert) as most of them use a standard tap. I use them for tooling and trade show displays where they see lots of use by people who don't pay attention to much and they have held up great.