MonoMonday:Pattern

Didn't know what to do for today's challenge and then I spotted this.

It's not terribly exciting but it WAS the only photograph I have taken today and I consider getting a blip from one shot a challenge in itself.

Apart from sharpening it is not processed in any way, not even converted to mono.

Do you know what it is?

Thanks chantler63 for a great job of hosting this month.