CORONA — These are the ties that bind — and sometimes break.

A straphanger spotted a plastic zip tie around a wheel on a Manhattan-bound 7 train car at the Willets Pt. station Wednesday morning — prompting her to tweet to the MTA out of concern.

Zip ties used on the undercarriage of a #7train..is this standard? How often are these checked for wear and tear? @MTA @NYGovCuomo @ABC7NY pic.twitter.com/V2WhtfQo2G — MsJaya_B (@MsJaya_B) June 28, 2017

"How often are these checked for wear and tear?," she asked in a tweet, which was also sent to Gov. Andrew Cuomo. She told DNAinfo New York she was "shocked" to see the flimsy ties in use. They were also on wheels on other cars, she added.

A spokeswoman for the MTA said the ties "are a back-up way of securing a cable (a secondary fastener) on the subway car" and is used with other fasteners.

It's safe and only used on some cars of the 7 line as they await new brackets, she said.

"We have a specially designed bracket that is being engineered and is set to be installed in the next few weeks," spokeswoman Beth DeFalco told DNAinfo.

The MTA has been under increasing fire from riders amid increasing system failures, from subway delays and infrastructure breakdowns to a host of derailments, most recently on Tuesday when an A train derailed in Harlem, injuring more than two dozen riders.

The MTA suspended two supervisors for not securing a piece of rail that caused the derailment, sending the train off the rails and into a wall, officials said.