Hi Wideford,

Only just seen this thread. I would add that it is comparable with other Black Mountains/Brecon Beacons standing stones in its flat slabbiness (that really is a word). Sandstone often makes for quite smooth-sided stones anyway (that might appear worked). It's also right next to a stream which would be the usual positioning for most of the standing stones in the area.

Examples of local slabby standing stones at Carreg Waun Llech ("Llech" means slab):
http://www.themodernantiquarian.com/site/11789/carreg_waun_llech.html

Nant Bwch:
http://www.themodernantiquarian.com/site/9574/nant_bwch.html

Maen Llwyd:
http://www.themodernantiquarian.com/site/9575/maen_llwyd_twyn_du.html

Tretower:
http://www.themodernantiquarian.com/site/105/tretower_stone.html

Standard Street:
http://www.themodernantiquarian.com/site/13563/standard_street.html

Neuadd Glan-gwy:
http://www.themodernantiquarian.com/site/9573/neuadd_glangwy.html

Example of local smooth-sided sandstone menhirs:

http://www.themodernantiquarian.com/site/4182/king_stone.html

http://www.themodernantiquarian.com/site/9571/maen_hir.html

http://www.themodernantiquarian.com/site/4248/battle.html

And some other stream/riverside standing stones in the area:

http://www.themodernantiquarian.com/site/348/fish_stone.html
http://www.themodernantiquarian.com/site/102/growing_stone.html
http://www.themodernantiquarian.com/site/3037/llangenny.html

Plus obviously the Daddy of all Brecons slabby waterside stones (a bit further away):
http://www.themodernantiquarian.com/site/104/maen_llia.html

All in all, I reckon the Pentre House stone fits nicely with the general type and location of the other stones in the area.