<p>Flaws in nuts that hold up lights throughout the Big Dig’s tunnels may be the result of workers overtightening the fasteners when they were first installed, a top highway official said Thursday.</p>
<p>Highway officials revealed this week that an inspector had discovered a cracked nut on a light fixture in the Ted Williams Tunnel in September. After further inspection of the Williams Tunnel and the Interstate 90 Connector and Interstate 93 tunnels, officials said they believe hundreds of fasteners throughout the Big Dig tunnels are flawed and must be replaced.</p>