SPOKANE, Wash. -- A pair of pliers. That's what the FBI says links Kevin Harpham to the bomb found at Spokane's Martin Luther King Day Unity March.

Now Harpham, who stands trial later this month for the attempted bombing, is trying to keep the jury from learning about those pliers.

During a pre-trial hearing Thursday it was reported that the FBI found tool marks on the bomb's electrical system that matches a pair of crimpers seized during a search of Harpham's property.

The FBI insists, under a microscope, those marks are as unique as our fingerprints, and the US Attorney's Office is trying to show that Harpham made the bomb used tools and materials later seized by the FBI.

Also during Thursday's hearing, prosecutors revealed the bomb's detonator was powered by a 9-volt battery. They said the wiring connecting the trigger to the explosive had been crimped together with a pair of pliers.

After putting the plugs under a microscope, forensic experts found the pliers had left behind unique tool marks on the connectors. Once Harpham was arrested his pliers were shipped to the FBI forensics lab in Quantico, Virginia to look for a comparison.

Out of 17 different pliers only one crimping tool, one made by a company called Klein, matched the tool marks the examiner found on the bomb's electrical system.

Now Harpham is asking the court to keep this tool mark evidence from the jury because it's too imprecise.

However the FBI agent who says Harpham's pliers are the same one used to make the bomb also uses tool marks to identify insurgents using IEDs to attack American troops in Iraq and Afghanistan.

Harpham's trial is scheduled to get underway August 22.