The beta match is required for the antenna to work properly.
The beta match parts for the MK3 are no longer available. But you can retro-fit your TH3-MK3 with the solid-rod "hairpin" beta match assembly used in the current TH3-MK4, which is much simpler than the aluminum tubing arrangement used on the MK3.
You can look at it in the MK4 instruction/assembly manual which you can download from the Hygrain web site at: http://www.hy-gain.com/man/pdf/TH-3MK4.pdf
You can order the parts from Hygain.
Contact their Tech Support - (662) 323-9538 - which I've always found to be very helpful.
Mel - KS2G