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May 11, 1995


Appeal from the Circuit Court of Williamson County. No. 88-L-187. Honorable Paul S. Murphy, Judge, presiding.

The Honorable Justice Goldenhersh delivered the opinion of the court: Maag, P.j., concurs. Justice Welch, specially concurring.

The opinion of the court was delivered by: Goldenhersh

JUSTICE GOLDENHERSH delivered the opinion of the court:

Plaintiff, Ronnie McKenzie, appeals from the denial of his posttrial motion for a new trial and his motion for leave to amend his complaint to conform the pleadings to the proof, by the circuit court of Williamson County. The underlying cause of action filed by plaintiff was a products liability suit based upon strict liability in tort against defendant, S K Hand Tool Corporation, for injuries plaintiff sustained when the ratchet wrench plaintiff was using broke while he was working on a truck, causing him to fall and injure himself. The case was tried to a jury, and at the close of all evidence, the jury returned a verdict in favor of defendant.

On appeal, plaintiff's principal contentions are that (1) the trial court erred in striking all evidence regarding defendant's wrench specifications, measurements of the component parts of the wrench in question, and plaintiff's expert witness's testimony with respect to those measurements and specifications and (2) the trial court erred in admitting evidence of an absence of prior accidents or incidents because defendant failed to establish the proper foundation for such testimony. We reverse and remand for a new trial.


Plaintiff was injured on September 10, 1987, while working on the engine of a truck at his place of employment, Uselton Sales & Service (hereinafter Uselton) in Marion. On the day of the accident, plaintiff was to overhaul the engine on a large over-the-road truck. To overhaul the engine, plaintiff was required to remove the heads, which were held to the engine by a number of large bolts. Normally plaintiff used a 3/4-inch air impact wrench to remove the bolts; however, after removing several bolts, the wrench developed a low-pressure problem. Plaintiff decided to use the 3/4-inch ratchet wrench his employer had in the shop. This 3/4-inch wrench was manufactured by defendant. Plaintiff broke two or three bolts loose with the ratchet wrench and removed those bolts with the wrench. Plaintiff, in attempting to remove another bolt, experienced difficulty even though the bolt broke loose. To remove the bolt, plaintiff put an extension on the wrench. While standing on the truck, plaintiff began pulling back the wrench. The wrench came apart and plaintiff fell off the truck backwards, hitting his right side and shoulder on the concrete floor. Plaintiff sustained injuries to his neck and shoulder.

When he got up, plaintiff found pieces of the wrench on top of the engine, in the frame of the truck, and on the floor. Plaintiff picked up all the pieces of the wrench and put them on top of the battery box. Plaintiff did not find the plug from the wrench. Plaintiff was alone at Uselton when the accident occurred. When David Couty, plaintiff's coworker, and Gene Uselton, the shop owner, returned to the shop, plaintiff told them about the accident and showed them the wrench.

Gene Uselton testified that the 3/4-inch-drive ratchet wrench was not used often in his shop and that he could not remember when the wrench was purchased. He did not know whether anyone had ever disassembled the wrench since he got it. Plaintiff also stated that to his knowledge no one had ever disassembled the wrench. Plaintiff testified that he had used this wrench before without any problems prior to the occurrence.

Len O'Connell, a manager with defendant, testified that the wrench in question was a 3/4-inch-drive ratchet wrench manufactured by defendant. O'Connell also testified that defendant made three other different-sized ratchet wrenches: a 1/4-inch drive, a 3/8-inch drive, and a 1/2-inch drive. The same design is used for all of these wrenches. However, some components of the inner body of the wrench are manufactured by other companies and purchased by defendant for use in assembly of the ratchet wrench. Defendant only makes the drive body, the pawl, the handle, and the reversing stem.

The inner body, or the driver, of the wrench in question fits into the housing of the handle. These parts are held together by a circular device called a snap ring. When the tips, or "ears," of the snap ring are pinched together, the driver can be removed from the handle. The snap ring holds the driver and the handle together. The spring in the ring is designed to insure the snug fit of the ring in the grooves.

Defendant has blueprints that contain the specifications of the sizes of each component of the wrench. The components are to comply with these specifications, which have a tolerance for each measurement. The part is acceptable if its actual measurement fits within the tolerance limits. For each part there are figures that represent its upper and lower limits. If the measurement of the part does not fall between the upper and lower limits, the machinist knows the part is not acceptable for use.

The component parts of the wrench in question were measured by four individuals, and the measurements were compared to those required by the specifications. Dr. Leon Dunning, a retired professor of mechanical engineering, and William Switalski, a mechanical engineer, measured the parts and testified as expert witnesses for defendant. Charles Reynolds, a registered mechanical engineer, and Hurley Johnson, chief inspector for a parts manufacturer, measured the component parts and testified on behalf of plaintiff. The outside diameter of the snap ring and its "ears" were measured when compressed at .56 and .59 inches apart, and the degree of hardness of the ring was determined using a Rockwell C scale. Also, the outside diameter of the snap ring groove in the handle and the outside and inside diameter of the snap ring slot in the driver were measured and compared to defendant's specifications. Plaintiff's expert, Reynolds, noticed a tapering radius on both the inner and outer edges of the snap ring groove in the handle. This taper was also measured.

Plaintiff's experts measured the hardness of the snap ring several times on a Rockwell C scale and got several different hardnesses ranging from 45 to 51 when the ring was measured in various places. Reynolds concluded that the ring did not meet the hardness required in the specifications (a measurement of 48 to 52 on a Rockwell C scale) and that this failure to comply with the specifications could affect the snug fit of the ring in the grooves of the driver and thus its ability to properly hold the driver and the handle together. Reynolds also stated that the variance in hardness found in the ring was the result of manufacturing and not use. Defendant's experts did not measure the snap ring for hardness.

Upon measuring the "ears" of the snap ring compressed at .56 and .59 inches apart, plaintiff's expert got a diameter of 2.269 inches and 2.280 inches respectively. Plaintiff's expert found the measurement of the outside diameter of the snap ring groove in the handle to be 2.3130 - 2.3125 inches. Defendant's expert's measurement for the same part was 2.315 inches. Defendant's specifications required 2.290 inches with a tolerance of .005 inches, so a measurement between 2.285 inches and 2.295 inches would be acceptable. However, the measurements obtained by both plaintiff's and defendant's experts exceeded defendant's specifications.

Reynolds, one of plaintiff's experts, noticed a tapering in the radius of both the inside and outside edges of the snap ring groove in the handle. Defendant's specifications do not mention tapering in the radius on the edge of the ring. Reynolds testified that it is important that the internal parts of the wrench comply with the specifications, particularly with regard to the snap ring and the grooves. Reynolds stated that it is common knowledge in the industry that the dimensions of a groove which retains a snap ring must be perpendicular and parallel and that the edges must remain sharp. Reynolds opined that a taper is like a ramp which allows the snap ring to be ejected. Also, in his opinion, the tapering was done during manufacturing and did not result from use. This point was affirmed by David Bidlack, engineering manager of defendant's Ohio plant. Bidlack stated that the taper is intended to prevent the cutting machine from dragging on the part as it comes back out of the groove. Hurley Johnson and Leon Dunning also noticed the tapering.

Regarding the possible causes of the accident, Reynolds offered two potential explanations for why the wrench came apart. First, Reynolds opined that the failure of the parts to comply with defendant's specifications would create a manufacturing defect which could contribute to an incident of the sort involved here. Specifically, the snap ring groove is not to specification, and the handle has a large radius and tapering of the edges. Reynolds suggests, as a second possible cause of the ...

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