Some of my PCBs in the past have used 1.8mm to accommodate slightly larger than spec PCB mount pins - if you've ever tried putting Gaterons or V1 Zealios into a PCB with 1.7mm holes, you'll know what I'm talking about. I know you probably think that was making Zeal60 preferentially catering to Zealios and you're right. Since Gateron was the biggest offender, and now they have fixed the bottom housings, I've reverted back to 1.7mm for Zeal60 rev 4 and future PCBs like WT75-A for Xeno 75.