All of TR's pillars come as standard with undercut or non standard without undercut. The advantages of undercut are that there is no need for washers in assembly and they offer a flush fit. This data sheet details the range of materials and sizes the spacers and pillars are available in.
Invinity to build 20MWh flow battery in UK
A surprising comment for someone who (I think you´ve said in the past) worked in the industry. National Grid have a variety of reserve service schemes...