Most modern cars are fitted with a synchronised gearbox in order to prevent the 'dog teeth' and the gear engaging whilst out of sync and crunching. A synchro mesh consisting of a cone clutch and blocking ring sees the cone clutch engaging first before aligning the gear.
Trying to change gear without fully engaging the synchromesh system or selecting the wrong gear will over time wear the synchro transmission parts. Great

synchro parts

for any car in the form of gears shafts, synchro rings, synchronisers, cone clutches and blocking rings are all readily available at Euro Car Parts.