July 22 - U.S. truckmaker PACCAR PCAR.O beat second-quarter profit and revenue estimates on Tuesday, helped by strong demand in its aftermarket parts segment as more truckers opted to maintain their existing fleet.

Shares of the Bellevue, Washington-based company rose 5% in the early hours following the results.

Cautious U.S. truck operators have been deferring new purchases due to high interest rates and market uncertainty, fueling demand for aftermarket parts and services.

"The North American truck market is being affected by economic conditions, the uncertain impact of tariffs and a soft truckload market," CEO Preston Feight said.

However, this rise in demand for parts and services has benefitted manufacturers such as PACCAR, which have been leaning on aftermarket revenue to counter slower sales of new vehicles.

PACCAR's revenue from the parts segment rose 3.4% to $1.72 billion during the second quarter from a year ago.

The company, which designs and manufactures trucks under brand names Kenworth, Peterbilt and DAF, also relied on cost-saving measures to combat earlier headwinds from import duties.

PACCAR reported quarterly adjusted profit of $1.37 per share, surpassing analysts' average estimate of $1.29, according to data compiled by LSEG.

Its second-quarter revenue of $7.51 billion beat market expectations of $7.03 billion.

(Reporting by Apratim Sarkar; Editing by Shreya Biswas)

((Apratim.Sarkar@thomsonreuters.com;))