VistaPlan drawing board issue – Can anyone help?

My companion began a drafting course just lately and wanted a drafting board. I purchased her a second hand one, measurement A1. She solely wanted A2 so I DIY'd it to make it smaller. I did a good job apart from one bit. The items that clamp to the wire don't keep clamped. Everytime you loosen the knob to lift the parallel bar off the drafting board it additionally loosens the connection to the wire. I believe I is perhaps lacking a spring washer or one thing. Does anybody have the identical drafting board and may be capable of assist? Thanks upfront.

https://preview.redd.it/96q1a2g6xija1.jpg?width=2250&format=pjpg&auto=webp&s=74c23396b3b53157555bf01f5754f7a8da70f17f