HSM

The HSM insert traces back, by thehackersparadise.com's account, to 1996, when Bobby Grace built the insert from what that publication describes as golf ball core material. The name, Hole Seeking Material, was the pitch: soft where the ball meets the face, firm enough behind it to hold its line. The same publication credits the insert with a competitive run worth noting, if not verifying, writing that HSM putters held all top ten positions in the same event. In 2009, per that source, the insert picked up a cosmetic update, with the HSM letters worked directly into the face itself.

That same year, bobbygraceputters.com dates the start of work on a successor. The HSM² Radial Face Insert Putter, arriving out of that development, is described by the maker's site as an improvement on the original, one built to allow early roll in addition to the distance correction the first HSM was known for. Two eras, then, separated by roughly a decade and one letter: the original insert earning its reputation in the late 1990s and into the 2000s, and the HSM² carrying the idea forward with an added claim about roll.

Reviewers who spent time with the original insert were consistent on feel. thehackersparadise.com called it soft, yet responsive, and you still get extremely good feedback with each stroke, and the broader Community read on the line echoes that: soft yet responsive, good feedback, forgiving on off-center hits. No comparable review commentary is on record for the HSM² generation, so the arc here is best read through what the maker's own materials say changed rather than through a second round of hands-on impressions.

What's clear from Bobby Grace's current product pages is that the HSM² insert didn't retire the concept, it multiplied it. The site now lists Mid Firm Grey and Tour Firm Black versions of the HSM² radial face, sold separately in different sizes for different head shapes, along with F-18 faceplates that let a buyer swap between a harder aluminum radial face and the softer HSM² inserts depending on green speed or ball preference. The insert, in other words, moved from being a single named feature to a modular system the golfer chooses and changes on their own.